MTN is a *******

I tried to get an upgrade on my current cellphone, thinking my contract ended in March, just to find out I have a bill of R1089. Their reason was that they continue sending me airtime and data after my 24month contract end. When I bought the the phone the very first month I did not use the mtn sim simply because I have a cellc number that I have been using for years and did not want to change, also because I think mtn is a ******* even though I did not use my mtn sim they double charged me for 2 months and said I used over my limit, which is impossible because that sim was not in any device. nevertheless I paid that R1089 and waited 2 hours in store for that amount to clear so that I can get my upgrade I'm still waiting and honestly I feel like just canceling and not dealing with mtn no longer. How do you sign up for a 24month contract and then they charge you for 27 months it's ridiculous. I'm sure 1000 of customers has left their network because of how they operate. I would like someone to get back to me and refund me for this.