Subsriptions added onto my account without my knowledge

I have had my number for more that 10 years and had no problems when it was prepaid. MTN called me to offer me a top up contract and that's when I experienced problem. I now has a subscription that I can not get rid off, regardless of all the calls I have made to MTN call centre seeking assistance. I have never subscribed to anything, one consultant told me that my problem is common with all other networks and there is noting they can do to assist me. MTN has been taking R3 from my account everyday making it +/- R90 per month over and above the agreed amount I pay every month for this contract. I feel that MTN is *****ing from me and I would like to warn other people who have contracts about these *******! I can not wait for this contract to end as I wouldn't want to attract a bad a record and at the same time I don't have enough money to cancel this contract. It is scary how these big companies are de*****ing us so that they can make their millions. If MTN is doing this to more than 1.5 or two million of their customers can you imagine how much they are making, please guys be careful!