Car troubles

There was a big problem with the car yesterday. The oil light came
on, even though i made sure that the engine always had sufficient oil.
It means that the oil isn't flowing through to the engine which is
really really bad. i don't think the mechanics that service the car
have changed the oil even though they said they did. (Or at least
thats what my dad told me). The reason for this is because the oil
seems like a really dark colour. Right now its parked in the driveway
until we and the mechanics can fit in a time for servicing. i really
don't trust the mechanics but my dad does. Hopefully it won't cost
too much. i really hope the engine isn't damaged much.