Got a Peugeot 406 problem, why nobody knows what is wrong?

The car has no obvious problems, in the evening parked the car. Two days later, go to the car, turn the key sound normal but does not turn over therefore the engine does not fire. Call the Rac, they cannot find tghe cause. They put many different testers and everything is functioning wiring, electrics etc They suggest immoboliser. We call diagnostics team, they cannot find a problem suggest secondary pump, third contact said maybe the brain of the computer is dead. Frankly, everyone has a different answer. We are stuck as we cannot tow the car, (car is automatic) and everyone walks away from the problem as nobody can figure it out.If anyone has an email address that I can get advice I would be grateful or suggest something here