I had the same problem with my 1st yorkie a few years ago & used Cowboy Magic Detagler - it was alot of work - it took a few days to get all the matts out. Just worked on him a little, then gave him a break about every hour.
I now have the matting problem on my 4 mth old puppy.
I started a thread on it last week - please check it out.
Mardelin helped me Greatly with those nasty matts!!!
http://www.yorkietalk.com/forums/showthread.php?t=85276