Call up your energy supplier and tell them about this (I presume your gas supply is not cut off?). They usually come out very quickly for this and if you have anyone vulnerable in the property (kids, elderly, disabled, etc) they will come out within 4 hours during their working hours (usually 8am to 10pm). Just give them a ring tomorrow morning and see what they say but if you call in the morning they'll probably get it fixed the same day. Only problem is that they can't give you a specific time so someone is going to have to stay in.
As for the money while you checked the debt did you check if it also used up emergency credit? Those are 2 separate things and it usually never above 5 quid which sort of adds up to what you said in which case you'll have a hard time getting the money out of them. Usually it's a good idea to reset the meter and get a new card when you move in, however, I know that's not always possible.