Debit order taken after contract was cancelled

We had a 24 month 2Gb data contract that expired and we physically phoned in to cancel this on the 4th of April 2015. I had numerous account queries while on this contract, which were never resolved.<br> The cancellation went through, because the sim stopped working shortly after. The ref number for the cancellation is ***. I have since had telkom adsl installed, and the mtn ****le with the sim has been laying in a drawer unused this past month. Last night (2 May 2015), a debit order amount of over R1600 has been deducted for this contract! The normal monthly sub was R120, how is this possible? I understand that there could be a final deduction for the past month, but there were no usage and also no penalties, because the 24 months have expired already. MTN fix this, I have 2 cell phone contracts up for renewal in June 2015 and will be looking elsewhere if this is how customers are treated.