MTN - Poor Service

My MTN contract expired at the end of March 2015. Since then I have submitted a termination request twice, been in store at both Mtn Canal Walk and N1 City and made numerous calls to their contact centre so that my contract can be terminated and migrate to prepaid service. Despite all this, no one has gotten back to me at all or processed the termination request, so MTN is continuing to bill me!! I have just received another another invoice for May 2015, despite the poor service I have received. The turnaround time for processing a termination request is 2 - 7 days. It has been 6 weeks and still no response from MTN. Absolutely pathetic service.