Cannot cancel Discovery credit card after 3 attempts!

I have tried to close my Discovery credit card on 3 occasions after paying more than owed on the balance owing, and today I again received a sms to pay an amount due ... which is bank charges after I asked for the account to be closed and paid more than what was owing. Telephoned 21 July case no. *** .. paid R200 ... told them NOT to phone me as unavailable during office hours ... they must email... received no confirmation that account closed; Telephoned 3 August case no. *** ... promised to email confirmation of credit card cancellation; Received sms for balance owing (after paying more than I owed) on bank charges incurred from 21 July ... telephoned again on 6 August case no. *** ... was told to ignore amount owing (I refuse to pay it as its bank charges accruing AFTER I gave instructions to close the account) ... and they again promised me that an email will be sent to confirm cancellation within 3 days ... nothing received; Received another sms today with another higher amount owing (more bank charges) ... I’m furious... just so frustrating that a simple task that any other bank can carry out quickly and efficiently... this bank cannot!