REALLY? BROKEN FLYWHEEL?

Well if it wasn't broken before, if the shop looked at it they might not have seen a problem. They probably didn't remove it from the crank so other than a quick look they didn't see a issue. It will be interesting to see where it's broken at and why if there's a obvious problem. If it's broken on the transmission side and the bolts were left loose you have a leg to stand on. If it's broken on the crank end and was never removed, good luck.