MTN still billing me after i cancelled my contract

I've had a cellphone contract with MTN which was due to expire 15 Feb. I called a month earlier to find out what the procedure is of cancelling a contract, but keeping my cellphone number as prepaid - I was told I'll only have to contact the call centre the day after my contract has expired and all the existing airtime and data will be taken and I was actually ok with it. Nonetheless I called on the 20th March due to busy work schedule and had forgotten about this and cancelled due to not being able to get through a couple of days earlier. I was given two reference number: One for Cancellation of the contract but keeping the number as prepaid. the second reference number was for the money that had to be reversed back into my account I was debited full amount which included the phone which was already paid for and had to be reverse.<br> <br> So last week Friday as I went through my bank statement I realised the cellphone contract amount went through again with additional money this time. I went to the bank Saturday morning to stop the debit order and reverse my money back. now I must deal with MTN again and do the cancellation of the debit order but I am not getting through!! how upsettin