If that contractor is located in Doha then go to the police with full details and file a complaint....they will be more than happy to take over.

If it's outside of Qatar then please ask them to send you details on the work "already" done so that you can confirm it. And also ask for their reepresentative here in the country (they'll come u with a STORY for sure)

They'll try to deceive you in any possible way....just stay tough and away from them.

Regards!!