RUINED MY CAR

My car is a 1991 Pontiac Grand Am.

I had taken my car to xpress lube after i was told they had cross stripped my drain plug. My car was in perfect condition. I have a 5 speed manual transmission(NOTHING WAS WRONG EVERY GEAR WORKED) i know for a fact because i had just got off the freeway. Then one of their employee's drove my car into the service bay to check my drain plug, comes out my car, goes inside tells me that my car does not go into reverse. After my car was working perfectly. since Dec 18, 2008. I have not been able to drive my car due to their employee not driving my car right. Breaking something in my transmission that does not allow my car to engage in to Reverse nor 5th gear anymore. When i shift to 5th it down shifts to 3rd it feels like. When i shift to Reverse it pulls forward. PROBLEM TO BE SOLVED: I would like my car to be fixed, due to their employee ruining it. Also i have witness that was present the whole time.