The 3 months period for moving to a location where the contractually agreed services cannot be fullfilled starts by the day you move (in case your movement notice is received prior to moving) or the day your notice is received (in case you notice VF after moving). Please note that it might be necessary to provide official proof -and- that it doesn't matter if the new address is within Germany or not.
In this case with the premature cancellation, your contract is ended 3 months after either your movement date (notice received before moving) or 3 months after your notice is received (notice received after moving).
If you cancel your contract regularly, it's ending at the day that the contractual term ends - no additional proof needed.
In both cases, it's the easiest way if you let open your bank account in order for VF to be able to deduct any fees from your bank account.
And keep in mind to send back any rental devices in time.