If the car is a 1968 or earlier model, then the body numbers will not match the VIN, this is normal.
If it is a 1969 or newer model, report it to the police & let them sort it out, the body may have been re-numbered because it is stolen.
You can sue to get your money back, if the seller did, or knew of it, it he can be ordered to pay restitution. If someone did it before him the police can track it backwards & see who first titled it this way, then you can sue him too.
There are also cases where the factory typoed the body numbers, so if it appears as 100011 & the VIN ends in 100001 as an example it could be a factory screw up.