Front Seat Belt Buckle Assembly problems of the 1997 Mercury Grand Marquis

Purchased a used 1997 Mercury Grand Marquis from roundtree Ford in shreveport, louisiana. I left with the vehicle and the driver seatbelt seemed to latch properly. I returned to the vehicle to run an errand and the seatbelt failed to latch. No matter what I tried the latch would not fasten to the belt. This has been reported to the rude used car manager billy flowers who did say to bring the car in for repair but that they do not have a policy that safety restraints be checked by service personnel prior to sale of a vehicle.

Driver's seat belt does not lock ,but the other 3 do. 2 back ones lock and keep getting tighter with every bump in the road.