MTN is robbing people

I took out a sim only contract at Mountain Mill mall, Worcestor - mtn store for 100GB anytime and 100GB night time. Every month my money is deducted from my account like clockwork but I did not receive all the data, when i tried calling the shop in Worcestor there was no answer for multiple days. I tried calling customer care and e-mailing them as well with a response every 5 to 7 days. When i finally deceided to get different internet and cancel the MTN contract they are not responding anymore. They now want me to pay a cancellation fee of R3000+ after they were the one's not giving me the full amount of data. They broke contract and now i have to pay.