Unresolved Termination, and Billing Issues at Vodafone

Despite my request and the fact that I returned my modem, Vodafone has not yet disconnected my internet service. I terminated my subscription to the Vodafone Internet service on the 21st of September, 2023, at approximately 4:00 PM. On the other hand, on October 2, 2023, the customer service department of Vodafone informed me that the internet service hadn't been terminated, that it was still operating even though there was no contract, and that they had billed me for it. They are sending out invoices in error, and the customer service representative is rude and disrespectful, suggesting that I file a complaint rather than helping me find a solution to the problem.