Unsatisfied with FNB and their debt collectors who do not collaborate.

I had an overdraft and handed to debt collectors. I have paid up the amount of R3780 and requested fnb to close the account they refer me back to their debt collector Wonga(as it writes on caller id) although they said they are Blake and associates. I called wonga collectors they said they will send the letter via email. Tull today they haven't so that means I have to pay the interest and fnb refuses to close the account. FNB are ****mers.