[72 four door]

I am a painting contractor and have been working for these perticular people for over 20 yrs.Ive always had verbal contracts with them,and payment was never an issue. They moved into a mcmansion and I had painted a few rooms just walls and ceilings and charged them about 600.00 a room. [these rooms are about 15/18 with boxed trim which were detailed with another color] last april they called and wanted more painting done. which consisted of the basement 75/30 the great room, hall,kit, ceiliing,walls and trim all 2coats. caulking all gaps and fixing nailpops golore. we started the job and the wife wanted the master bedroom,bath done basement bath,and bigger shoe molding installed and the piano room ceiling repaired. add 2200.00. So then were on the job and shes wants the guest room done, laundry 4 baths, and I,m putting paint swatches on the walls so he knows whats going on. basically I did the whole house and I finish give them the bill 3000 in paint and 18000.00 in labor . it took us 3 months to do. The husband freaks and just gives me 10000.00 and wants to get other bids I guess to find out if my prices are fair. Do I have any rights? geez I busted tail and feel so freakin screwed. I just don't know what to do.