Bob, I will try & help you if I can, DO NOT TURN THE ENGINE although the damage has now been done, I don't know if your son is aware of what's involved with a belt changed? the Adjuster should show signs of being new ( If they changed it as it's behind a cover with a different part No to the Original one) lso the belt should have the ID Numbers if it was a new one, they should still be present & to be seen, the indication of Sludge / Dirt /Grit / removal in & around the Block / Rocker Cover / Hoses & their Clips, If you have the Receipts bob, there is a lot you can do, but on saying that, how many miles has the car done since the belt was changed in the 2 years as you state