Terrible service at FNB

I am very disappointed in FNB. I have a personal loan with them and had been in arrears due to financial constraints. I had made arrangements to pay the arrears off and I am now back to paying normal installments. FNB had handed over my account to Barrett & Associates, who even after I have sent countless emails indicating that I have paid off my arrears and tried to contact them have not responded to me. I went back to the FNB collections department who are now telling me that they cannot do anything about it if it’s handed over. Can you PLEASE sort it out. I am debited for the monthly instalments AND by your lawyers who have not communicated with me. Reference number FNBPE321066