Product: Debt collection

My mortgage was sold/transferred from Nationstar Mortgage to XXXX XXXX XXXX in XX/XX/XXXX. I have made mortgage payments to XXXX XXXX XXXX without missing a payment since this transfer although I was under Chapter XXXX Bankruptcy since XX/XX/XXXX. I was discharged from the Chapter XXXX Bankruptcy in XX/XX/XXXX. I began receiving phone calls from XXXX XXXX XXXX that my mortgage payment was 30 days delinquent. I informed them that I had been under Chapter XXXX Bankruptcy but my mortgage was not under the bankruptcy and I had continued to make mortgage payments throughout. I forwarded 2 years of payment verification to them and they responded in writing on XX/XX/XXXX, stating they had received my information and was researching my account. Next they mailed me a letter stating the there was a payment due XX/XX/XXXX and it had not been received and they were charging a late payment of {$12.00} to my account. I then phone them and request a manager, I was connected to a supervisor and I explained my problem. The supervisor when over all of the payments that I made since the account was sold/transferred to XXXX XXXX XXXX and discovered that a part of the payment I sent for the XX/XX/XXXX in the amount of {$470.00} had been applied to {$420.00} in foreclosure fees. The supervisor said the foreclosure fees came over with the account from Nationstar Mortgage. I informed the supervisor that my mortgage had never been in foreclosure, but that I was aware that Nationstar had tried to submit a claim through the Bankruptcy Court that I had missed 3 payments in XX/XX/XXXX. I explained that I had never missed a payment on the mortgage and that I had documentation from Bankruptcy Court that the motion was withdrawn after I provided payment verification to the Bankruptcy Court. The supervisor advised me to forward submit my documentation, which I did on XX/XX/XXXX. XXXX XXXX XXXX then responded to me by letter stating they received my correspondence, researched my account further and removed the fees. They also included a corporate advance history for my account documenting that {$420.00} in fees listed as a beginning balance had been charged to my account on XX/XX/XXXX and that a credit in the amount of {$420.00} had been applied on XX/XX/XXXX. The corporate advance history also showed XXXX other fees had been charged to my account, {$420.00} in FC ATTY Fees on XX/XX/XXXX ; {$270.00} in Bankruptcy Costs on XX/XX/XXXX ; and {$150.00} in Bankruptcy Fees on XX/XX/XXXX. This same letter also informed me that my account was still delinquent and due for the XX/XX/XXXX payment, although I had mailed a payment in the amount of {$510.00}, which was credited to the account on XX/XX/XXXX. I phone XXXX XXXX XXXX again on XX/XX/XXXX and requested to speak with a manager and after explaining my problem, I was told that the fees came to them with the account and that a manager was not available at that time and someone would return the call to me. I have not received a call from anyone from XXXX XXXX XXXX as of date. My mortgage has not been in foreclosure and there was no claim from Nationstar nor XXXX XXXX XXXX  listed in my Chapter XXXX Bankruptcy.