mtn bad service providers

I've been with Mtn for more than 20 years. it started when I changed from prepaid to contract. but due to financial experience I had to cancel contract and take my number back to prepaid. I paid penalties. only to find that they didn't concil my contract and demanded me to pay R700. I did pay that amount and confirmed it's been cancelled. now they sending messages to remind me to pay R1535.87. and that my contract will be cancelled in November. MTN is not what I thought it is. they are very very bad