over payment while on debt review and struggle to get correct response or money the owe me

In 2009 I was placed under debt review. An amount of R15 888.65 was given by FNB as a COD outstanding amount. The amount that was paid from 2009 to October 2016 was R 23 593.50 An over payment of R7810.07 was made!! FNB's latest response was that no payments was made after 09/12/2016!!, that was my response after I've emailed them regarding the OVER PAYMENT of R7810.07

I please want FNB to review my agreement as with the debt collectors in 2009, acknowledge the fact that I've overpaid and make that payment a.s.a.p