regarding the food, dont feed him for a day or 2, and then drop a few pellets in, obviously they float, so the ones he dont eat you can pick out. but i wouldnt worry because oscars are pigs, they will eat if hungry, dont worry about that.
but honest mate, give him time.
the only other thing it might be, is if he's getting spooked.
sudden movement can scare the fish,
where in your house do you have the tank? is there alot of people around it all day? if your tank had 2 lights turn 1 of them off and he might settle quicker.
how big is your tank and what pleco do you have? maybe your pleco has had a go at him and freaked him out abit.
i wouldn't worry at all though mate, give it time.
but yeah try him on the pellets after 2 days and he should come up for them.
good luck mate
also... turn your temp up to 27/28.