Had a lot of work done back in April on our 2000 SSei. Immediately after work was performed the oil gauge indicator dipped close to red. Also began to hear engine knocking. Never had these issues prior to work this most recent work being completed. Returned the car to the repair shop 5 days after the original work was completed. I am trying to recall the exact sequence but I think it got towed back to the shop because it had stalled. They indicated that we needed to replace the oil pressure pump. Seemed to coincidental and we wondered if the repairs that were done had caused the oil pressure issue. During the second visit they said that our battery needed to be replaced and they replaced the oil pressure switch and oil lube filter. They wanted to replace the oil pump but we wanted a second opinion. We have not driven the vehicle much since April as it developed a intermittent engine knock. Here is a list of the work performed and the original issue identified. Any advise on how to proceed is welcome.
Labor: CODE PO442 Leak in Evap system. Also wires arking to plenum leak at manifold gasket. Smoke evap system to find leak. R&R line and vent valve with hose. R&R valve cover gasket, R&R intake manifold gasket, R&R hoses and thermostat, R&R wires.
Parts: Evap Line with Scrader connector, evap vent valve, evap vent line, intake manifold gasket, valve cover gasket, belt super charger, thermostat and gasket, upper and lower rad hose, heater hoses, reservoir hose, vac hoses, coolant flush, set n ignition wires, brake light bulb.

Had someone else look at it. They thought that it needed an oil change and replaced the oil. They did not have all the history of the work we had done (my mistake) and thought the oil pump should be replaced.
What should we do? We did not have low oil pressure until right after the original work was performed. Did they get coolant in the oil? Need help on how to proceed.