Product: Credit card or prepaid card

A {$89.00} payment was not posted to my account back on XX/XX/XXXX for the amount of {$89.00}. However, they have cashed that payment of {$89.00} and never posted it to the account. I have called Synchrony Bank about this dispute numerous times and have spoken with many different representatives and was finally told in XXXX of XXXX that it was being applied to my account and that my new balance on the account was {$41.00}. I called in XXXX to request all my statements and was mailed 91 pages and I went through every single statement that they sent me to make sure I wasn't overpaying and saw that my {$89.00} payment on XX/XX/XXXX never got posted to my account back in XXXX. When I spoke to XXXX the representative in XX/XX/XXXX as well as numerous other representatives about this discrepancy, she told me the {$89.00} was going to be credited to my account and my new balance was {$41.00}. So, on XX/XX/XXXX, when I got paid, I mailed a money order in the amount of {$41.00} and wrote the words " PAID IN FULL '' on the memo portion of the check along with the account number. They cashed and applied that payment to my account. ( I also have disputed this with the credit bureaus as well. ) Yesterday XX/XX/XXXX I received an email from Synchrony bank asking if I missed my payment and saw that the {$89.00} was posted back to my account! I do not owe that money to them and this account is Paid in Full! By law, " payment in full '' will discharge the debtor 's obligation entirely, under the legal doctrine of " accord and satisfaction ''. Tendering of a check marked " payment in full '' or " paid in full '' is an offer to settle the debt of an amount different than what the parties ' contract says. Cashing the check is considered to be acceptance of the offer and extinguishes the debt. In order to be effective, the words must be clear and conspicuous on the check. There must be no doubt that the debtor intends the check to settle the debt entirely which I have done. ( This is quoted from the XXXX XXXX XXXX XXXX XXXX XXXXXXXX ). I understand once a check is cashed and deposited to my account when with said words " PAID IN FULL '', my obligation has been met, and this agreement has now been closed and paid in full. The odd thing about that {$89.00} credit that they said would be applied to my account in XX/XX/XXXX was posted to my account was then marked as posted on XX/XX/XXXX, WHY? Why was it posted in XXXX when I contacted them in XX/XX/XXXX about this? Something is not adding up correctly and my Excellent Credit is now going in the opposite direction because of this dispute and that makes me furious. I pay every bill on time on the XXXX of every month when I receive my XXXX check. I have outstanding credit and pay my bills on time every month. I take great care of my obligations and I am proud of that. I also have checked the XXXX and this company has many discrepancies against them. I will also be filing this with the XXXX as I am very stressed out about this situation. Every time I call Synchrony Bank, I get different answers and excuses and it's very aggravating to say the least. I'm hoping that this gets resolved in a timely manner as my credit is dropping significantly because of their error.