Welcome to Vodafone Community
The first bill is sent within the first week of joining and you will be charged pro rata for the data used. When an account is cancelled, this will also mean you will have no further access to online billing.
Providing the direct debit is still in place and not cancelled, any overpayment will be paid direct into the account. For this reason, you need to keep the direct debit until you have received the final bill with a zero balance.
I think the best option to get this sorted would be to use Live Chat or ring 191 from a phone with a working Vodafone sum in or ring them from the landline number. Just ignore the prompts to key in your mobile number and after the 4th prompt asking you to it should change to say press 2 for contract customers.
Landline Tel :03333040191
I would be surprised if any charge would be levied as Vodafone would need to support why they are charging the fee.
If you have received communication on a missed payment I would also suggest checking your Credit file to see if anything has been reported on it. Experian offer various options to get a copy.
https://www.vodafone.co.uk/explore/network/network-satisfaction-guarantee/ holds info and faqs.
It's generic advice given on the forum not to cancel the DD until the £0 bill and Sorry Your leaving letter has been received.
Also until any Credits or Debits have been sorted. It usually takes Vodafone 2-4 weeks to send a final bill by post.
Im sure Customer Services will be able to help you with clearing this up.
Signal strength i.e. 2G, 3G or 4G is depdndant on location.
If you cancelled the direct debit, you will have left Vodafone without an account to repay any credit.
Having mentioned that, if you use live chat, they will be in a position to confirm the final amount owing and make arrangements to repay any amount owing back to you.
It is still important to make sure you are sent the final bill with a zero balance. This is your confirmation that the account is closed.