MTN is very dissapointing treat customers unfairly

On 29 April I called MTN to let them know that I am not receiving my data and they give me the ref nr. The consultant promise me that they will investigate and come back to me within 3 working days. I waited and went to their store in Kagiso Mall and the sales lady send the email with no response or acknowledgement of the email. I send several emails and make calls with no respond again from MTN. I want to know how does it take to investigate for MTN? If I stop paying I will be blacklisted and what about MTN no it will continue taking my money. What do I need to do to make MTN respect and honour the agreement. MTN is one useless company with no respect for customers what so ever. The contract number 808 is not working. I hope to receive respond from MTN or do I need to stop paying because MTN is not respecting the agreement we had.