Vodacom - poor communication and bad service

I used to had a Vodacom Account and was cancelled after the contract expired in March 2016. In September 2018 i get email about debt collection agency Nimble Group that there is an amount outstanding. This was a debit order account and i have used same bank for over 18years, why was the acount not debited? Why was i not contacted? Is this how your treat your ex-clients?

Current clients be aware that when you become an EX client that you are not over charged or handed over for debt collection without any communication.