If this is subject to an ongoing criminal investigation this forum may not be the place to seek the answers to your questions. Presumably this could end up in court and you would require somebody, an "expert witness" to speak to those questions and answers in court.
The questions should be put to BT by the Police and BT should be able to give the correct answers to the questions and will be able to back those answers up with credible evidence.
All Police Forces have a communications/data liason officer who should be able to progress this.
BT Fon or whatever it's called now, has a limited reach in distance. So a potential hacker would need to be pretty close. Also to use Fon they would need a bt id. Naturally they may have got that from social engineering or other nefarious means.
As for hackers breaking things, frankly this sounds like a local security problem. So you need to make sure your own systems are properly protected. Before changing passwords etc, everything needs to be clear, otherwise a keylogger could pick up the changes.