I am so dissatisfied with MTN service

I am disappointed with MTN service. My father has been on contract for years now with MTN , last year August he cancelled his contract with MTN and they assured him the contract has been terminated.. Funny enough they are still deducting money for the phones though the contract is canceled. We went to MTN stores but they said we must call MTN customer services, we have been trying to call MTN customer service but they do not answer their line. what makes matters worse is that they locked both his phones.