Pet Care Needed

I rescued a male shih Tzu off the side of the road and he is Matted . I've tried to trim it myself but haven't been able to. I also took him to a grooming place In my area and they wouldn't do it because I don't have papers on him & don't know if he's had his shots. Also He's matted worse on his legs and head than other places, Which I thought was weird.