Product: Credit card

This dispute is with my Citi Thank you preferred card. 
My first attempt at disputing my claim was during XX/XX/XXXX thru XX/XX/XXXX I believe, when I was doing my taxes, going through my statements which I have not been paying attention to as I have not used this card in a while and have been trying to pay it off. Much to my dismay, I discovered this company has been charging me an interest rate of 29.9 % instead of my normal rate of 17.74 % from XX/XX/XXXX though XX/XX/XXXX. 
So I called in and spoke to a representative and asked why the rate was so high and he told me it change in either XXXX or XXXX of XXXX because of a late payment. I proved to him my payment was indeed NOT late, and he agreed and reduced my rate back down to the normal rate of 17.74 %. 
Furthermore he stated he was removing the late fee and I would see the credit of {$30.00} on my account within XXXX business days. 
Well that NEVER happened and I never received that credit. I then asked him since we agreed that I was charged an incorrect late fee and incorrect higher rate, I stated you owe me for 5 months of interest of 12.25 % on the outstanding balance for the past 5 months ( The difference between 29.9 % and 17.74 % ) and I would like that credited back to my account as well. He stated he would credit XXXX interest back only, but that was not good enough. Why would I accept getting charged interest that was incorrect for ANY amount of time. That's fraudulent!. 
I explained as I have before several times that the problem ( Or what I call, Citi 's nice little scam ) that I make my payment every XXXX, XXXX XXXX days BEFORE the due date, It gets put in the mail the same day. The problem is, this company receives all their payments to a XXXX XXXX XXXX So if and when they decide to go to their XXXX XXXX XXXX if it's NOT XXXX and all of those payments are not recorded in a timely matter or on the same day, Those who do not get opened and recorded, get a late fee if their accounts receivable people don't do their job. I have told this company XXXX times when this has happened in the past that they SHOULD be looking on the post marked date from the post office to see in fact when it was received and sent out. 
Furthermore they should be looking at the date the check was written to see if it was written XXXX the due date. Now I'm aware there ARE some people who XXXX fudge this when they know they are late, BUT I AM NOT XXXX OF THEM! And while you could fudge the date on the check, our good ole United States XXXX XXXX certainly WILL NOT fudge their post mark date! 
But Citi Cards does not care nor do they take intelligent steps to make sure their GOOD CUSTOMERS do not fet unfairly charged late fees and get their good interest rate jacked through the roof. It really is a nice scam!. What I find funny is they could simply avoid this problem and adopt a XXXX day grace period. But why would they do that since this little scam works so well for them apparently? To further prove my point, my bank XXXX XXXX  allows you a 10 day grace period. My insurance company allows a 10 day grace period, so do several other companies that I do business with does! So anyway back to XXXX XXXX of my dispute ...... 
So he transferred me to a supervisor who was not polite, who was a nasty person and basically she wasn't going to credit anything, even though her rep before her was trying to fix the problem and told me he was crediting the late fee. So this turned into a nasty call on both ends admittedly, So we ended the conversation and much to my surprise I looked at my statement again on XX/XX/XXXX and no late fee was refunded! So I guess the nasty woman supervisor even took away what her employee SAID he would do which was to at least remove the incorrect late fee. 
So I called back again on XX/XX/XXXX, asked for a supervisor and spoke to another XXXX unqualified supervisor. I explained what happened and explained that I have had to contact them several times over the history of my account with them for this very same reason. I explained that I have been a longtime customer, a GOOD customer that has NEVER missed a payment, always pay more than the minimum due and I an outstanding XXXX XXXX of XXXX!. 
This supervisor after going back & forth had the audacity to tell me to stop using the United Sates Post office to mail my bills! Way over stepped his bounds! Then he also stated that in looking at my account they had already credited me ( XXXX ) times over the past 12 months and that's all they were allowed to do in a 12 month period! 
Now that is also an incorrect XXXX  statement as I stated over the last XXXX years of doing business with Citi, XXXX have had to call in many more times in a 12 month period to correct this very same problem. And every time they did it without fear or favor. 
So when I realized I was getting no where with this XXXX I asked to be transferred to his supervisor... If you can call them that .... 
So then I spoke to a woman and she basically told me the same thing. Only this time, she stated they \were only allowed to do a XXXX XXXX  courtesy credit in a 12 month period. So which is it? XXXX time, 2 times, 4 times 6 times .... It really should not matter if the customer proves to them they were in fact in the wrong. But these people and this company could care less! 
What is most appalling to me is their ( SO CALLED ) Supervisors are untrained at actually making the customer happy and the most important part is ... KEEPING THEIR CUSTOMERS!!!!! 
So in closing I am asking the Consumer Financial Protection Bureau to FULLY AUDIT MY ACCOUNT SINCE INCEPTION .... And I want my unjust late fees ALL returned to my account and I want my XXXX moths of unjust interest on of 12.25 % which was charged on my outstanding balance credited back to my account. 
Furthermore I would hope and pray that The Consumer Financial Protection Agency Bureau, investigate and audit ALL of Citi Card account members and see for themselves just how many American account holders they are scamming! I am QUITE SURE that the agency would be shocked to discover all of the fraud and mismanagement going on within this company! My hope is to get this resolved immediately without any further action taken on my part, as my next move will be to contact the Attorney General in the great state of Missouri and inform them of how this company operates within this state.