Unjustified legal threat 8 months after cancellation for 2 month ago account!

I have received an e-mail from a debt collection company that failed to do their homework properly before falsely threatening legal action against me from MTN for an account that is overdue 2 months now. Therefore this account will be from January/February 2016, correct? I forwarded the confirmation e-mail I received from MTN that they received my 1 month notice (that was also sent 12 months previously already, stating I would end the contract after 2 years on due date for renewal) & MTN stated in this e-mail both my numbers is permanently cancelled on 10/09/2015 that they only sent to me on 09/09/2015. This was not the end of contract date that MTN chose to end earlier as well as my reoccurring data was simply just lost that I paid for. I got a new Vodacom number that was used since cancellation of both the other numbers & these sim's destroyed due to my numerous monthly complaints for 2 years of poor ********* service received from them that I would never use MTN services again. Why would there now suddenly be an account of 2 months ago outstanding but no account since 20/09/2015? So who did MTN give my old number now to? This is once again a serious warning to people NOT to have any contract with MTN.