Impossible contract cancelation

I have a cellphone contract with MTN which is now expired and in such I am on a month to month basis to now. I was contacted by a MTN representative before the contract expired who gave me two options to either upgrade or toe cancel my contract. I opted to cancel my contract and thought that would be the end of it. To my disappointment it was not, they kept on deducting money by means of a debit order. I then contacted customer service which then referred me to call 135. I was on line for more than an hour in order to cancel my contract and still there where no operators available. I just want to cancel the contract as I have no need for it, this process in so frustrating en led me to write this review. Please can anyone just assist me with this matter.