the whole thing is BS and the usual crappy excuses. JB will be able to confirm but afaik all engineers should have keys to the cabinet otherwise how are they supposed to fix anything?
If I were you I would give them one more go and if they muck you around again or can't fix it then send a letter of complaint to the CEOs office detailing everything. If it was working before common sense dictates something has changed to disrupt the service and they should know/be able to work out what it is. When techs start to not turn up and appointments gets changed then you know something dodgy is going on.