Oil level light or oil pressure?
Have you checked the oil using the dipstick?
When was the oil and filter last changed?
Has the car done very high mileage?
What kind of garages are you taking it to, there is an oil light flashing and beeping, yet they are telling you there is no fault?? At the very least you have a faulty oil sensor causing a false alarm, at worst you have an oil supply and will very soon have a totally wrecked engine!! I hope you did not pay these cretins.
vaux
November 2009