FWIW, when other customers have posted their replies from the resolutions team on here in past topics, most of those VM responses have been totally incomprehensible or irrelevant nonsense.
If your next bill goes out on 28 Nov, and disconnection on 11 Dec, you should be able to follow what is going on with the final billing in real time and take any evasive measures as necessary.
Your predicted bill of £64.82 on 28 Nov seems to be in line with what might be expected under VM's billing scheme for disconnection. Once 11 Dec has passed, and you are disconnected, you should expect to see that final bill with the correct amount of refund due to you a few days after your disconnection. If that doesn't happen, you may need to take further action at that time.
I have no connection with VM but some general observations from past 'gone-wrong' disconnection topics on here, which might help you, seem to be ...
When you return the kit (wherever that may be dropped off) get a receipt for the items you drop off with a tracking number. Once you have dropped off the kit, that is your only proof it has gone back to VM. I would also note the serial numbers and MAC addresses of anything you send back so you can check against any future demands from VM. Send the kit back as soon as possible because it can take a long time for VM to collect it and sign it back into their system as being returned. Personally, I would also photograph the items and the packaging you sent it back in (for proof of what you sent back and the fact it was well-packaged if you are using DIY packaging). Complaints about not receiving packaging have been common on here and, if you are moving home, it is very possible that VM will continue to send packaging to your old address when you have moved.
It is understandable that people want to cancel their direct debit ASAP to prevent VM taking disputed amounts of money. Those who do that, before all dealings with VM are concluded, often seem to run into problems in topics on here if VM thinks it is still due a DD payment. Past topics have often described former customers having credit defaults logged against them over a disputed VM final payment. Keep good offline records of all VM's final billing demands for future reference.
If you are moving home, and not taking a VM service with you, a further reason to keep the DD in place is to do with getting the refund from VM electronically rather than by cheque. Past topics have described former customers moving home and VM sending the refund cheque to their old address, where the account was based, even when the customer had provided forwarding details.
All of the above is nothing more than my own personal opinion so use at your own risk and make your own decisions based on your own circumstances. My own view is that the info from Kath_P above is reliable and is what you should expect to happen. Keep tabs on what VM is up to as your disconnection progresses and take further action if things look as if they are heading off course from what is expected. Communicating with VM on here happens in slow-time but the results are usually more reliable dealing with the VM forum team than using VM's other channels of communication. Good luck!