Bad service

I had a very bad service with MTN, since I had 1 cell phone contract and Sim only with them from 2011 till to date, on the 21 April 2023, one of the consultant called me to inform that my sim only is due for upgrade, I told her that I am no longer using that sim. After call we didn't agree with anything, to my surprise on the 28 July 2023 Mtn deducted R6961.00 from my account, I immediately called them to try find out about that amount, a consultant at collection told me I had done early upgrade on my account, rather she said I cancelled my contract, I explained that I did no such thing, I tried to lock a complaint with her but she referred me to ***** department, I have been struggling to sort out this problem until two weeks ago where someone told me that early upgrade was done by Mondo agent, I should talk to them, I did that and Mondo investigated and told me it's true their agent did a mistake in my account, now Mondo said they have send a request to MTN for reversal of early upgrade for my account to be back to normal but still I am been sent forth and back, in the meantime my number keeps on be suspended due to the so called arrears that I didn't do, mind you my cell phone contract was supposed to be ending on 28 October 2023, but I owe Mtn this big amount, my name is on ITC, this is really bad