Cannot close account and get them to collect cylinder

Cannot close account! I sent them an e-mail that I do not need their service anymore and they can close my account on 24th Feb 2022 and they can collect their cylinder. It is a month later and they still send me a bill. Phoning is useless you do not get through. E-mailing is also useless because they just escalate to somebody and then they never come back. About 20 years back I had such good service from them! Now avoid AFROX if you can because their customer service is non-existent!