Bad service

I have been taking Toyota Avanza there for 3 years. Suddenly my car has a oil sump problem. They are been servicing my car for 3 years, they never raised that issue. Someone messed the bolt nut treads of the oil sump. Now I need to get a new oil sump. They are money driven here, excellent service comes last. When they say Someone messed the treads.I have never had this problem before and then the qoute me for a new oil sump.