Poor customer service

My contract with mtn ended in June of this year.i had an outstanding balance of R7000 which i paid in full at the store in Bloemfontein. I requested that my contract be terminated at that time but because mtn was on strike the legal department could not be reached. I made various attempts to reach them and i even have the email correspondence. I have been continuously billed from June till present for a service which i have not been provided with.the number was deactivated by mtn legal ever since. Ive even tried to find out how i can resolve this issue with the mtn 808 number and no one has been able to help me.as my contract ended and i requested that it be terminated i should not be held liable if mtn was on strike and could not complete my termination. I now have a huge bill and im seeking legal advice.