Charged for a years worth of service that had been cancelled

My telkom account was paid up and cancelled over a year ago and today I get a call saying I have been handed over when I had cancelled the service in June last year and the worst part is they are saying I owe them money when I haven’t received an invoice in a year nor have I used any service of theirs I have proof of payment and all the invoices but they still are insisting that I owe them even when all the proof has been sent to them already I am absolutely disgusted in the poor customer service and day light ******* that telkom is trying I will never take a service with them again.