Ham-fisted idiot "mechanic" owes you a chaincase.
This would be my take on it. FWIW I have two chain case bikes, one is metal one is plastic. I have had the metal one bend by a so called mechanic that had no clue on how to remove it and tried used a larger screwdriver as a pry bar. Fortunately it could be bent back.
If you need a replacement chaincase, best place I have found to order them is
Dutch Bike Bits. They also sell the tarp/frame ones that fietsbob refers too.
Aaron
