Hi there Louspage and welcome to the forum
I hope your bankruptcy went smoothly at the court. It is nothing to be worried about if your case is sent to an Official Receiver who is not local. The Official Receiver's office is operated by the Government department called the Insolvency Service. As with everything these days they are having to deal with cost cutting. As a result the OR is having to close local offices and consolidate into more regional centers. Ultimately this makes no difference to you.
It is quite normal for the first contact with the OR to be within 24-48 hours of being made bankrupt. Sometimes you get a call the same day. Normally in first contact they just want to agree a mutually convienient time to conduct a full interview with you. When this is depends on how busy they are and when they can fit you in. You mentioned you have your interview on Monday which is within the week you went bankrupt. I would say that is very normal.
As far as your car is concerned the Bankruptcy rules state you are allowed to keep a car worth £1000 or less as long as you need it. You can find more info about this here: My Car and Bankruptcy