Vox - Billing you after the account closed !

After canceling my account (***) with Vox Telecom, I was never informed that the router had to be returned. I was contacted out of the blue and asked to return the router, months after canceling the contract. Arrangement was made for Aramex to collect the router from me, which was done on the 1st of December 2020, Waybill Number ***. After more than a month, I received bill from Vox Telecom for payment for the router that I had already returned to them. Numerous phone calls, being passed from pillar to post, I managed to speak to someone that said my account (which is supposed to be closed) will be credited with the amount supposedly owed.