Let down by MTN South Africa, this is embarrassing

Hey I subscribed to MTN LTE data plan where I pay R150 for 60 gigs per month. The nightmare started when the cut the in and out going calls from my SIM card with out my consent. Then the data is an on and off mode with out me knowing what is going on. When I went to MTN store i consulted with an MTN agent in Century city in cape town who told me there is nothing he can help with bcz I sign up with a service provider. I am so confused and when calling the MTN services via 136 none of the agents are able to explain and give a solution to my frustration