Vodacom cancelation nightmare

I recently canceled my contract with vodacom and I paid the settlement amount and month end will be debited the last premium amount according to what I have been told via sms. But now I'm receiving calls from MBD(with their bad line) saying that they are calling on behalf of vodacom. I called vodacom to understand why am I being handed over to debt collectors and they couldn't assist me, they said that the account is probably in arrears that is why because they can't see anything on their side. My account information is blocked and they can't help me I must call MBD. Why must I speak to a third party that I didn't have an account with and what were the reasons of them handing over my account as if I'm in arrears. I don't recommend anyone to be still taking contracts with vodacom.