MTN poor network connectivity between 6pm to 10pm in the evening

Hi, I am using MTN data plan from almost six months but from last month the data is not available between 6pm to 10pm in the evening everyday. I am located in Upper Houghton, Houghton Estate, Johannesburg, Gauteng. I have complained several time but the network coverage staff is saying that they are fixing the network towers. I am fed up with the poor network in the time when our president advise us to work from home. I wanted to cancel this plan and now they are asking for the full settlement of the amount for the leftover period of my data contract. Can someone please help me with this?