Unauthorised upgrade of my contract

I am so sick of MTN I have a contract with them and last week on the 17th I got a call from their Sales Consultant who offered me an upgrade on one of my numbers. I told her I don't want to upgrade and she went on to do an upgrade, basically she misled me to think she is just doing verifications. Now they are sending from pillar to post when I want to cancel that upgrade. I have sent them an email, still nothing done. I even called them 5 times and their *********** employees can't help me. I am going to cancel all my contracts with them. Very poor service from such a big brand.