Sounds like these tangles will have to be dealt with by the vet.
Might be useful if you could train him to let you groom him. Try really short sessions. I trained Polly by constantly tickling her behind her ears while brushing her. As long as I tickled, she put up with it; but when I forgot and stopped, she jumped off. Now she associated being brushed with something else, so the tickling isn't necessary, but helps!
I think there are some pinned vids about this on Health and Behaviour.