How to groom a cat that has gotten soaked with cooking oil?

Not sure, but because he howls when lonely, I think a neighbor poured cooking oil on my male cat named "Pac Man" for the design on this sides. (looks like a PacMan) He is not too keen on being brushed, tried the towel, it worked to get the heaviest oil out. He has long fur. Two layers, it is soft like bunny fur. He has a few mats too and not sure how to get those out as he bites me if I pull even the tiniest bit. Any advise is welcome. He is usually pretty good at grooming himself, but this oil is overwhelming him and it is something I need advice on. Maybe oatmeal or cornmeal?