Contract expired and haven't heard anything!!

I have a tablet contract with MTN ***) and it expired on the 17th May 2015. I called before then to change to prepaid and was advised that I need to call on the 18th May 2015. I called on this date (***) and was told it will be done and somebody will be calling me. It has been over 2 weeks and I have heard nothing. I have legally ended my contract and should MTN try and take money from me after I have paid my last debit order I will see you in court for *******ly *****ing money from me. Make sure it is now on pre-paid and have the decency to inform me that this is the case!! Also respond to my previous compliant as I have been trying to upgrade my other line for 2 months!! I have been getting a thousand excuses from you useless people. Fix your problems and stop making your issues mine. My money still goes to you without a hitch but the service you give is absolutely *******!