When I took the car out of storage in April the car ran great for the first part of the day. Then when driving at night the oil light came on. I checked everything out and added oil to the car. The light went out and ran okay for about 15 minutes.
After getting it home the next day I drained all the oil out and proceeded to do a engine flush to the car, once the car got warm the light came on again and I shut it down. I drained everything out and proceeded to drop the oil pan. The oil pan would not drop for me, so I had a repair shop look into the job for me. They stated the book has 3 hours for start to finish for dropping oil pan and replacing all the gaskets and assembling. The shop calls me the next day and states that they took 5.5 hours and got it back together and refilled the oil, for which I provided. Then they took it for a ride. They state that while the car was cold, no oil light; but once it warmed up the oil light came on and stayed on.
I would assume that the oil pump works at this point. They are hearing no noises at this time.

How should I proceed with this?
I don't feel that I should have to pay the excess of hours because they didn't do something right, considering I had everything all apart for them and labeled up.
What should get done or checked at this point and does it involve a lot of time?

The car has been for sale since the winter and I have thrown a lot of new major parts into the car over the past 18 months.

???