Robbing clients their hard earned money

I have been using mtn network for years but I'm so disappointed.. Went for an upgrade in the store told they were having problems with the system.. Went back home without the device.. To my surprise every month they deduct money from my account of which I don't have a contract with them.. Now 5 months been told my matter is been escalated so they can refund me.. Upto now nothing.. I'm so so disappointed a big company like that don't care about customers.. If I go to the store I'm told the management is dealing with the matter.. But no results