Welcome to YorkieTalk. I like your Yorkie's name, Wiggly.
If the matting is really bad, I would spare your pup the agony, cut the coat down and start again. Be careful with electric trimmers; they can catch a mat and pull the skin and cause injury. You may want a professional to carefully scissor cut first.
Mats and bad tangles have to be taken care of before shampooing and conditioning, otherwise they tighten when wet and are more difficult to undo. For really bad tangles, I use the sharp end of a metal rat tail comb to carefully pick apart the hair. I always hold the hair with one hand to prevent pulling of the skin. A little dab of PetSilk Silk Serum also helps pull apart tangles. I'm not sure if you have PetSilk available to you where you live. You could also try simple cornstarch. Apply dry to dry hair and don't let your pup eat it.
To prevent matting, stay on top of the tangles daily. If Wiggly wears clothes, you have a lot more work on your hands.