2000 Chevy Impala LOW OIL PRESSURE LIGHT

Hi Ive just recently took my car in to get the whole collant system fixed and supposly it got fixed all for 1589.00 and now my LOW OIL PRESSURE Light is on to my car and makes alot of flapping noise when pressing down on the gas peddal and makes a loud knocking sound when starting up the car. So it went back to same shop now theyre telling me that its because my "Barrons" are out something like that. Does this seem right to you