Contract terms changed without my knowledge to get more money out of me

I have been a loyal customer for over 10 years with MTN. I renewed a contract and we agreed on a price, when I am being billed it is a totally different amount & contract. I tried to call the contact center and I am being told no one can help me. This seems to have been done on purpose to get more money out of me, MTN you better get a hold of me before I go legal with this.