Handed over to debt collectors after being told my contract was cancelled and no amount outstanding

I called Vodacom in February 2016 to cancel my contract that was expiring as Vodacom was billing me for data bundles to the value of R500 which I did not request or approve. I went through the lengthy process and was advised it had then been cancelled.

In June I started receiving invoices again including the data bundles that I had not requested nor approved. So I called Vodacom again only to find out my contract hadnt been cancelled as originally advised. I managed to get them to agree to credit my account as this was their error and cancel the account for good.

Now in Feb 2018 I receive a SMS and Email from a debt collector saying that I have been handed over. I have not received an email, phone call or even a SMS from Vodacom about any amount outstanding or any invoices since last year June/July.

I am at my wits end and will be taking this further and getting more senior parties involved.