Disappointed in MTN

I am very disappointed in MTN. Have been with MTN for more than 4 year. I have upgraded in February to an R159 3GIG data. Didn't get any invoices but took so much money from me and MTN kept on suspending my service. I investigated on my *** number and found that they charged me for the R175 upgrade and charged me R132 for the hardware fees also. Its now been 3 months and still have not been sorted out. Have been at the Middelburg MTN store and all they can tell me is that their service is down. MTN is owing me R425.26 At this stage. I would like to terminate my contract as I am receiving the poorest service. MTN is so fast to take your money but they cant pay me back my money. I would like to have all my money back as I know its getting to month end and they are going to take my money gain. I would like to know terminate this contract.