Product: Credit card or prepaid card

My complaint is with my Capital One Master Card, ending with XXXX, that is branded for XXXX. Although I am able to use this card anywhere ; I only use it when purchasing from XXXX due to the rewards earned with XXXX purchases. 
I am complaining about {$8.00} interest that was charged on my statement for the period XX/XX/XXXX through XX/XX/XXXX. The reason I was charged this interest is because I deducted the {$23.00} statement credit redeemed the previous month from the total balance due of {$850.00} on that previous month 's statement. 
When I opened this account XX/XX/XXXX, the documents that I received stated that my rewards could be redeemed for statement credits. 
I am enclosing a PDF of documents that explain this complaint. 
On the first page of my PDF you will see circled the various ways my rewards points could be redeemed one of which is a statement credit. On the second page of the PDF which is also part of the agreement document on page one, you will see that I have highlighted : " Promotional offers may allow you to pay less than the total New Balance and avoid paying interest on new transactions that post to your purchase balance. '' Continuing on the following pages, I am enclosing copies of a few recent month 's statements with the rewards for that period written in by me with the confirmation number acknowledging my redemption credit and no interest charged for anything on the statement even though I short paid the previous balance by the amount of the previous month 's rewards credit. The first statement I included was the XXXX XXXX statement. 
Moving along to the next two pages you will see that on the XXXX XXXX statement I notated the same reward redemption credit and new amount to pay. Here you will again see that no interest was charged and on the second page of that statement you will see that the credit I used to short pay the previous month was duly credited with no problems. 
Again moving along to the next couple of pages you will see this same pattern where I redeemed my rewards for a credit, deducted the credit and short paid the balance due with no interest charges incurred. I will add that I have been doing this for most of the months that I have been using this card. Some of the earlier months, I deducted the rewards points from online purchases. However, I switched to this method many months ago because it gives me a better understanding of my actual rewards credits. 
However, the trouble started with my XXXX, XXXX statement. Here you can see that I was charged {$6.00} interest on the short payment of the {$15.00} rewards credit that I had redeemed the previous month. I promptly called Capital One 's customer service and the gentleman apologized, told me it was a mistake, and promptly issued me a credit for the interest charges. 
However, I was again charged interest of {$8.00} on my latest XXXX XXXX statement because I short paid the total balance due of {$850.00} by {$23.00} which was the rewards redemption amount. Again I called customer service and asked for a refund and an explanation of what was going on. I told them that if they had changed the rules, I would just have to wait until the following month when the redemption credit appeared on my new statement to take it. However, I told them that I was not happy because I had been doing this for a long time with no problem and I did not understand why they were changing their policy. I say " them '' because I talked to several people during this call and each one said that they WOULD NOT issue me a credit for the {$8.00}. 
I spoke with two supervisors and employee number XXXX, XXXX, was especially " harsh '' to me. 
I am very upset about this, over the way I have been treated more that the amount of interest. I never pay interest, and I do not this recorded on my credit report. My credit score is in the XXXX 's and I take pride in my conscientious handling of my finances. 
I am requesting a credit of {$8.00} to be issued to my account, an apology given, and any trace of interest charges erased from Capital One 's credit reporting.