Cell C fibre / Greencom arrears situation

I signed up for fibre to my home with Greencom. They were taken over by Cell c fibre, the debit orders carried on going off my bank account but the service deteriorated. Many days of no wi fi later I cancelled with cell c fibre last week adn they confirmed the cancellation. I did ask about the invoice that showed I was in arrears to Cell C. I sent through copies of my bank statements showing the debits to Greencom had been taken off my account but then today I receive another invoice of R3015. Can someone please tell me how I sort this and with whom ?? I have been dealing with Lynthis Morrison