Product: Credit card or prepaid card

Capital One assumed control of my XXXX XXXX XXXX on XX/XX/XXXX from XXXX XXXX XXXX XXXX XXXXXXXX. Prior to this transfer, a payment was made for the entire statement balance of {$1600.00} on XX/XX/XXXX through the online payment mechanism in place at the time through XXXX. Please review a copy of the attached e-mail with a payment confirmation # of : XXXX. Despite my payment, and the entire account history of paying each months statement balance in full, Capital One has not credited this payment to my account, and in spite of hours spent with Customer Service, there has been no progress made at all in resolving the matter. 
On XX/XX/XXXX between XXXXXXXX XXXX and XXXX XXXX, multiple calls were made to Capital One XXXX XXXX Customer Service at XXXX, on several occasions the system would report wait times of over an hour, and the system would ask me to opt into a call back when a representative became available. On the 2 occasions when I elected this option, the system would call back with an automated message that advised me to hold for a representative, and then the call would disconnect prior to any representative becoming available. After numerous calls, your customer services representatives reported they did not know how to help me, and could only enter a note. I had been requesting a case be opened and that I be able to submit electronic correspondence which would confirm the payment. However, I was advised your online system had no ability to upload documentation and that only a supervisor could open a case which would allow e-mail or electronic submissions. I was finally transferred to a supervisor, XXXX # XXXX, and she was rude and completely unhelpful. She reported she would not open a case, and at first suggested that I trust her that it will all get worked out. When I asked for some written communication to commemorate this reported trust, she reported she could not do that. She continued to report that the system was not recording old data yet, but when I confronted her with the fact that it is recording pending charges, she amended her position to say it was not processing previous payments. When I asked how this could be when I now am being harassed by Capital One via texts and e-mails that I have a payment due, and none is due, she then incredibly suggested that I should take this up with XXXXXXXX XXXX, the prior account managing institution. I advised her that her position held no merit, and I strongly advised her to take action by opening a case / dispute/ or review to address this error. I further advised her verbally, and hereby do advise you in writing that any inaccurate negative credit reporting made Capital One against me would be in violation of Fair Debt Collection Practices Act ( FDCPA ), and would be followed up with vigorous litigation. 
I do hereby demand a forthwith crediting of my paid balance on the account that you assumed from XXXX XXXX XXXX XXXX XXXX. If XXXX XXXX has not properly forwarded these funds to you, then your issue is with the, and not trying to impose an already paid debt to me. Forthwith movement toward this demand is highly encouraged, or litigation and Consumer Financial Protection Bureau ( CFPB ) filings will proceed. I have recently locked this account and will be in touch with XXXX  Regional Director to advise them of the grossly unsatisfactory experience I have had with their cards transition.