For a mechanic to pull BS like that is crap.
He caused it, so he should fix it at a reasonable cost
If he has no solution then he an't very good.
Ask for your money back or take it to someone that can sort it and charge him for the repairs.
I won't quote the consumers guarantee act to you, but you know where I'm coming from?
Cheers,
Edit;
Welcome.
Best to intro your self on your first post