MTN bad service

My name is Monica Mkhwa****. Biggest mistake i ever made in my life was signing up for an MTN contract. I canceled the contract on time within the 10 days cooling off period which they said I wasn't gonna get charged for it. This was in September till today the contract has not been canceled and they want me to pay R790. Everytime I call I'm being told that the R790 will be taken away from my balance as it was a mistake but till today that has not been done instead I get threats that my name will be take to the credit bereu. I've spoken to Amanda from the contracts cancelation in October already, I then spoke to Chantal and Npbuhle as well and they all promise to sort it out but they haven't. They don't call me back to keep me updated and I always have to follow up. MTN is the worst