MTN GONE BAD

I'm disgusted with Mtn I had a contract with them for many years now when I decided to opt out they playing tricks. My contract expired in October and I sent them email to say I don't wish to continue even went to the store I was told to call 135 I did that but when transferred to cancelation department they don't pickup. In December they called me and I opted for a Zero rate option in order to keep my number, later they decide to give me data and now they handed me over to debt collectors. I never received any account notifications and when I ask the guy if they have a new contract with me they give me a run around. I will not leave this lying I will take them on because I did not sign any contract and so I don't owe Mtn anything now they are tarnishing my name for their benefit never