mtn:very *********** and useless

i had a contract with mtn that was supposed to end in may 2018. when i went to the store to cancel my contract as i was nearing the end of my contract and i did not want an upgrade, i found out that my account was **********ly upgraded without my consent. As a result, i could not cancel my account, had to pay an increased premium for a phone that is not even in my possesion. I called Mtn and they told me to send an affidavit with my id copy attached. I did exactly that and i was told the case will be resolved in 72 hours. 5 months later my case is still open. everytime i call mtn,i am being told that the case is still open and there is nothing that they can do because the case has been escalated to the ***** department. i do follow ups on the case every week but there is no positive response.