Product: Credit card or prepaid card

Below is the letter I sent to Citicards, which explains all of the details : My Payment always due each month on the XXXX Ive never been delinquent to Citibank, and for the couple of times I was one or two days late, I paid the hefty fee of {$35.00}. But for the record, I have never been over 30 days past due, which is what is reported to the credit bureaus.
Being a loyal consumer since XXXX has become more of a detriment to me lately.
OnXX/XX/XXXXmy Credit Limit was still as it has always been {$3100.00} On XX/XX/XXXX I made a payment in the amount of {$2500.00} On XX/XX/XXXX your company suddenly decides to run a credit check on me and decrease my spending limit based on delinquencies to other creditors That is what I was told when I called, but dont believe it for ONE second. It is clear and very obvious to everyone that Ive spoken to that this is being handled as a reprimand for me being a conscientious consumer trying to pay down her debt and increase her credit score, as now you can no longer collect quite as much interest per month from me, so now I must pay the consequences. Again, just to underscore how sure I am of this reasoning : My payments to YOU are on time Those other creditors you are referring to if you bothered to check the truth are debts that I disputed as invalidThat is why they havent been paid. As the credit bureaus should be removing them, since the creditors were not able to validate them.
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So, suddenly, on XX/XX/XXXX, I make a large payment of {$2500.00}, and the way I am rewarded for that as a loyal consumer is by dropping my credit limit down to {$600.00} which then makes it look as if Im : 1. Over utilizing my credit with you FALSE!
2. Going over the Limit by {$74.00} FALSE!
Several, and I mean several inbound and outbound calls were made surrounding the 48 hour period of that large payment by many different customer service agents from Citi who were concerned that there may be a security breach of some type. Okay, sure some stranger kindly decided to make a large payment on my account balance? Come on now, these excuses above dont even make any sense. Say them out loud once or twice. Its clear you want the interest. And dropping a LOYAL consumer from a {$3200.00} limit to {$600.00} isnt a bit extreme????
This is completely unacceptable to me as I am being a responsible consumer who wants to lower her debt, and increase her credit score ( which by the way your two moves above did the opposite ). Why is there a punishment for that? Is someone at Citibank at risk for not getting as high of an annual bonus for this? I can not even imagine another reason. And please dont patronize me by trying to explain that you randomly pull credit reports on an annual basis. While this much may be true, please re-visit the second set of bullet points, and youll see why this will not hold as a valid excuse.
And as if the above isnt ludicrous enough, in of itself, you have the nerve to charge me the standard interest rate {$38.00} based on the entire previous balance of {$3100.00}, along with a {$14.00} over the limit fee?
Im pretty confident that I can find enough social media sites, and mom blogs, as well as the Fair Credit Reporting Act would be able to assist me further.
This is the most unfair treatment I have ever seen by a company as large as yours, and all you have to do is make this right, but since Im not 100 % confident that is going to happen, I will be submitting complaints to The Consumer Financial Protection Bureau and the FDIC as well.