Contract Renewal Nightmare

I am disappointed and beyond sad about how MTN has treated me. I was contacted by an MTN agent letting me know that if I wanted to renew my contract I could even though it was about 3 months early. I asked the agent multiple times about extra charges because we all know if you renew you contract early there is extra charges and every time I asked he told me no there is no extra charges why would we (MTN) charge you a MTN customer more money when you already a customer. So stupid me I renewed my contract and also extended it from 24 month to 36 months......To my surprise when my bill arrived I was told I owe them R1200 something. I called MTN and was given another nr to call and log a complaint. Which I did, more or less a week later I received a call back that the complaint was in my favour and MTN was supposed to credit me. At the time when my bill arrived, I paid about R400 something towards MTN because that is what the agent told me I would be paying per month, even cheaper than my current contract bill. After the call from the guys I logged the complaint with told me it was resolved, I had nothing to worry about and a credit will go towards my MTN account..........once again I was the stupid one. Received my bill for this month and again my bill is over R1200 and my service has been suspended. I can not even call 132. Thank you MTN for showing me once again I can not trust anyone. If there were any extra charges I would have waited for my upgrade. I am at my last, wit's end, tired of people treating me like a doormat and I"m at the point I just want you guys to come to fetch this phone and leave me alone will my contract expires and then need to be renewed. So disappointed in the way that I have been treated after being a loyal MTN customer for more than 20 years.