Inability to get contract terminated

I have a contract with Mtn. Am here in Eastern Cape. Contract has expired last year. I asked them several times to cancel the contract as I'm not planning to renew or upgrade. They said I should cancel on phone using ussd string. I think it's a load of crab coz I had a contract with another company and I just went into cancel after the contract ended. They never gave me hassles. Am sick of Mtn now