Poor service bt mtn

My contract with mtn ended 4months ago.i then went to south gate mall to upgrade as i left i thought everything was finalised.my contract was a package of 40g data for 229.first mnth was debited 357 i kept quiet then second mnth again 357 was debited.u called in to ask why is 357 debited instead of 229.they told me the guy at south gate did not complete the contract hence my bill is now too high but i was told the matter would be fixed.another month went by again 357 was debited i phoned once again only this time i dnt want any upgrade but to cancel my contract now i was told they cant cancel my contract cause of the contract upgrade tht ddnt go through.they said im must give them my phone numbers and the matter would b dealt with.still no answer.i guess i would b billed these 357 for life.im really disappointed.