I am looking after a bichon shih tzu mix for a neighbour (for two months). They told me they will get him groomed when they get back and not to groom him. They didn't leave a brush or anything for him either.

He has mats all over him and his collar can't come off because it's matted into his fur. He doesn't like being brushed. Is there an easy way to at least get the mats out?