Immobiliser fault

I have a 3008 1.2 e tech, until recently it's been OK ( since a wet belt replacement at 30000 miles?) Had the fault immobiliser fault come up on the screen...nothing would start break where locked, this motor was not going to move. Was told by peugeot agents to disconnect battery and leave overnight, done, no affect. Had to get the tow company to lift and take to agents for them to look at. I'm feeling this could be an expensive repair....anyone else had this....I rather think this may have the technicians scratching there heads.
Del