Bad Service Delivery and Lack of Accountability

My account from NHC was handed over to CNBDS and an employee from CNBDS mentioned that I should pay the account to NHC. He sent me the account number where I deposited an amount of R818.00. Then 2 weeks later I get an automated message that the account is still owing. I called CNBDS and the lady I spoke to was a supervisor and asked me to resend proof of payment. A week later, another similar email saying I'm still owing. This was since October 2020 and to date even after confirming with NHC that they received their funds, they still continue to send me emails, they keep blaming this or that.