Disgusting MTN Service

I have signed a data contract with MTN in February 2020. The contract states I should receive 20 Gigs daytime and 20 Gigs night time. To my surprise I have been receiving only 5 Gigs. I have been forced to pay R259 p/m to MTN for the service they are not rendering to me. I sent MTN an email to cancel the contract but they acknowledged receiving the email and never came back to me. I went went to different MTN Stores but there was no help at all. I made calls and you will hold for 2hrs without an answer. I logged a call at MTN Cresta store they said it will be sorted within 24hrs but this never happened. I have been to MTN Boksburg,Sunninghill and even their HO in 14th Avenue but no help. I am worried cause if I am going to reverse my payments it will feflect negatively on my credit scores