unauthorised debit order as eft done

I have had a credit card for many years incuding a cheque card , mt credit card was always paid by myself with not the miinumum payment byr more.In March 2015 for the first time , paid an amount of R5000 as the minumum payment due was R133 and the card diviision wnt above that and debited my cheque card for the full amount of R21000 which returned as ther was no funds. Firstly i have paid and who gave them the instrustion to debited by card again and further to this i received a sms notifying me that minumum payment of R274 is due by the 7th April and now to find out i was againe debited on 25March but my slary gets pai on 28th which leave my account unpaid again. The disgusting service that i am receiving , leave me in a option to close my cheque accoutn and move to another banking institute. Disgusted! Disgusted!