Please cancel the contract! !!

First of all I don't understand why mtn has a call centre cause they hardly help their customers! I took 3 cellphones on contract in march 2013. I have been trying to terminate my contract from early march up until now. I called mtn more than 4 times requesting that they cancel the contract. I called and I was told that they are going to cancel the contract and I will still keep my numbers. The lady told me that my last debit will be on the 30 of April which was fine with me. So on the 13th of may I received data bundles and airtime which I thought mtn was just giving me as a loyal customer. I did try to call 808 for days with no success. I received statement from mtn today which took me by surprise. I am getting sick and tired of mtn. I didn't include mtn on the budget because I knew that I was done paying. I checked my debit order and it clearly states that mtn debit order will still run for 6 months. How is that possible? I am confused and will not pay for this month! I really regret the day I took my cellphones on contract with mtn. I just want this contract cancelled and another thing I dont want to be listed on itc meanwhile the contract is finished!