There will always be a final amount on any contract. If you had left the direct debit in place, the payment would be collected in the normal way, and is likely to be correct. If there's an error, you can get your bank to reclaim the money through the direct debit guarantee, though do remember that this will leave an unpaid amount the service believe is due, so you would need to resolve that as well. It's generally better to speak to the network first.
Your screenshot would appear to show that your line has been cancelled, and the online account will disappear completely once the account itself is clear. If you want to pay a final bill manually, you should be able to do so by speaking to customer services. You'll need 07836 191 191 rather than just 191 now that you're not on Vodafone, of course. At the prompt for your number, just put in random digits until the system gets fed up and offers you an operator.
The final bill is always sent by post simply because the online account is closed when the number is transferred. For anyone coming to this thread later, please note that the address used will be the one Vodafone have on record for you. If you are also moving, the bill may not reach you and this has been the cause of unpaid amounts in the past.
