2001 Other Chevrolet Models 2001 Chevy Metro, fuel pump and

Our 2001 chevy metro had the engine replaced. When the mechanics brought it back I realized that oil was leaking. They came back and picked it up. Told me it was an oil pan gasket that needed to be replaced. After they'd had the car for a week, the head mechanic called me and said that they noticed two additional issues with the car. The fuel pump needed to be replaced and the transmission was slipping and had I noticed that the car was having difficulty starting at times. I told him the car had always started and we had not noticed anything unusual with the transmission. My husband and I went and picked up the car. I realized the next day that the car starts fine when its cold, but is horrible when its warmed up. Plus when it's idling and then you put it in reverse, the car dies! Now the mechanic isn't returning our calls. Can you tell me what could possible cause a car to start fine when cold but have difficulty after its warmed up and what can cause an engine to turn off when you put the car in reverse?