For Vodafone to take over the line you would of been notified with 14 days notice, BT would of tried calling you, sent an email, letter and a text message informing you another company is taking over the line, some people miss the call or don't have a mobile to recieve the text but emails and letters are hard to miss, did BT notify you and did you ignore it ?
BT can cancel the takeover if you contact them before it's too late, the cutoff is before 2pm 1 working day before the takeover.
If you were not informed of this then you could try calling tomorrow and ask if you qualify for 'priority back in service'.
If you were not notified then you have no way to know about the takeover, so you would qualify for priority back in service, BT will be able to verify as all notifications sent are logged.
Ring 0800 800 150 and ask for the connections team, they're the team who can authorise an expedite of an order and refer you to the priority back in service team.
A random company can takeover the line though, BT are not to know you're not switching providers, also people move out of properties and forget to cancel services, so new occupiers then place working line takeovers, that is why it takes 14 days to switch, so you can be notified and stop any mistakes happening.