Debit orders go through but 'disappear' on the system

This company is giving me grief,seriously i dont know any other platform to air my frustrations. I stopped using my fnb cheque account but didnt close it so i accumulated charges over R4000. This company called and told me to pay the balance in installments of which i did and finished. Even one lady an 1 guy confirmed it but said they cant issue a settlement letter they are waiting for fnb to allocate the payments. A year down the line im getting threatning calls,sms and emails that i must pay the the balance (the original balance) everytime i tell them i finished paying they ask me to go to fnb. Today i spoke to one lady and actually asked to speak to the manager because the story had changed now, now i owe R2000 and they have no record of my debit orders or any other record for that matter. I stayed on the line for more than 11 minutes waiting for the 'manager' and finally hung up. Everytime i phone them i hear different stories so now im confused as to where my moey was going all this time. My bank statement can bail me out,i did pay.