Valves on head damaged and timming belt ok.

Tell your mechanic that valves don't just get damaged without an apparent reason. I too would have guessed a broken timing belt. But if it's still intact, then it may be stretched and worn enough to "jump timing" enough to hit the pistons. These fabric timing belts are to be inspected and possibly replaced at 100K miles. Replacing the belts can be done for $500 and up but removing the head and replacing the valves is about $1400. Anyway, a "cylinder compression test" can confirm damaged valves. If they are into it that far, let them do the repair. Hold them to their diagnosis being correct, and replace that timing belt while it's apart. I'm sorry about your misfortune. Next car, get an engine with a timing chain, they rarely break.

Maybe the belt slipped several teeth.