I wonder would this also fall under the area of criminal activity since they purposely canceled the check for non-related issues?  Theft/fraud guised as under unsatisfactory service.  But you have the tracking number that shows you sent it back.  Call Fed-Ex and find out who signed for the package, then go to the Secretary of State, for that state, and find out who the principles are in the corporation, and start putting foot prints on people's foreheads as you work your way to the top.  Small claims court could also be an option, or an ethics violation reported to the land title association they belong to or to ALTA if they belong. 
Good luck and let us know who things work out.
       Jay