Paid up account

My account was handed over in January, which I paid in February. Now in October I get a call from different collectors informing me my account has a balance of R1700. I called the collectors and sent them a proof of payment and I told they can't trace the payment, I must call capfin to get more information. When I call capfin, they are telling me to call the collectors. I have also sent proof of payment to capfin and have not gotten any response.