Hey richardkenyon, definitely sounds a bit odd 😕 Best to chat with our billing team as they'd be able to double check what's happened there and get it fixed up.
It really doesn't sound like we've been of much assistance there. Would you like us to take a look from our end? I'm more than happy to have a good look through the account and confirm whether or not we've overcharged you.
If you cancelled your service on the day of your billing cycle, you'd have still received a final account to confirm its closure. Accounts aren't settled on the day you decide to disconnect the service. Feel free to send us a PM with your details. I need your full name, DOB and former account number.