Non-existent service by MTN all the way to top management.

I have a data contract with MTN that is inoperable and have reported this to customer care, service faults etc. without an improvement in service, only the normal automated computer responses. I have requested cancellation of the contract, again with no response. I then reported the problem to the MTN ***** department (after all, MTN is perpendicular *****, charging subscription fees without giving the contracted service) and they did respond, forwarding my emails to the relevant MTN departments, asking them to do something. Again, no response. This has been going on for months. In desperation, I finally emailed the MTN CEO twice on his corporate and private addresses: NO RESPONSE AT ALL. If anyone can advise on some way to get this company that markets excellence in service to respond, it would be appreciated.