Disgusting service

Cancelled my account for end december 2024, returned my free to use router and it was received on 14/01/2025. Now i get billed 1k for it!!! Sent them proof of delivery and receipt on 17/01 but still get invoiced. and all i get on the chat line is we are escullating the query, will take 24-48 hours. but no feed back and you cannot call them either everything must be done on chat line or whatsapp, utterly useless