Credit Card Settlement

i had a credit card with african bank, i settled the account on the 21st of APRIL, i called the bank to request that they close my account, the lady that i spoke to said it will take 48hrs for it to reflect on their system and i should call again then, which i did and was told that they will process my request. On the 24th i was debited R1200(R810 the normal installment amount and R390 per arrangement), i queried this and they said my acc had not been closed yet and no request what logged of such a request, i explained to the consultant what the case is and requested that they refund me as i've now overpaid them. i was told that by monday or tuesday i will have the money back, which was not the case. i had the money reversed on the 29th April and they did a refund on the 4th of May. i called them and arranged that they debit R810 imm and R390 end of May to repay them. R810 was debited as agreed but apparently R390 was no debited end of May as agreed,to my surprise i got a call on the 3rd July to say my acc is in areas and i have a settlement amount of about R600. How am i owing R600+ when the Bank didn't run its debit nor advised me of such? Who is at fault for this?