If your pup is matted to the skin, start fresh. Trying to work out a mat that's to the skin is not only painful for him but is almost impossible. Especially if he's been bathed couple of x's & the mat has shrunk & formed into a hair cement.
Take him to the groomers & have him shaved down. It will grow back.

You can request a #5F blade cut on the body (use #10 only for matted hair that's to the skin- because a #5 blade won't go through it), scissored legs, whatever face shape/cut you want.
If he's only matted in small areas, you can get a small mustache/nose scissor w/blunt ends from a beauty supply store & snip into them before you work it out w/a comb or pin brush. Like mentioned above, you can use corn starch (harmless to hair) or any kind of conditioning/detangling spray (spray directly on the mat).
The importance of pin brushes (no balls @ the end) or combs is that it can penetrate into the hair, to the skin & loosen tangles. Make sure to test the pins on your arms b4 you make a purchase bc some are not beveled & it hurts. The Madan brushes I sell has beveled pins.
Thank You everyone for recommending toplinepet's Madan products!