Can anyone help me?! I have two yorkies, one has a silky coat (so easy to groom!) and our puppy has a cotton coat. I am going to pull MY hair out! Our puppy Pippo (cotton coat) has tiny mats on his bum and legs. I can NOT brush them out

. I have used every brush I own and nothing is working, or makes the hair a little fluffy then gets separated and I can see the little clumps again!!
I currently use a Madan pin brush that I bought about a month ago. This is the only brush that doesn't make him cry and bite the brush! The only thing is that it is not getting these little mats out. I also use a boar bristle brush, comb (good luck) and do have a dematting comb but I think it may be wrong (the teeth are about 1/4 apart and the hair goes between them)!
I also use a detangling spray when I brush him by Paul mitchell for dogs.
I just dont know what I am doing wrong

?
Any advise would help! Thank you!!!!!!