Reno's puppy coat just about drove me mad until I found Iv San Bernard's PEK conditioner. Combing out puppy mats would take me an hour to do. But using the PEK conditioner cut the time down to 15 mins or less.
Puppy mats can be so frustrating, but take heart, they grow up and their coat grows out quickly.
Some more advice, do not comb/brush him out with a dry coat, it will break and damage the hair. Spray him with a detangling spray (you can use watered down hair conditioner) before combing out.