I have found if it's matted it's probably already let go from the skin and can be pluck or just picked out.
Combing would do the same, for one clump, I'd just pick away at it until it was gone.
I have a funny story about such.
When I first got my late Cody he has a matted clump on his back down by his tail, and his owner was calling it, jokingly his extra tail.
After he had adjusted to living here I took a little pluck at it and out it came, extra tail gone. She said he had it for years.
