I have a Siberian kitten (13 weeks old) and he has several mats very low in his fur and close to skin folds. Even if I wanted to trim or cut out the mats, this really is not possible due to the location of the mats and the inability to separate them completely from the folds of skin around his ear and in his armpit.
I had the same problem once with my cat.
Usually I can groom the fur with a special brush my vet gave me. Some bigger mats I pick apart with my fingers and then run the brush through. But if the mats get really thick and/or close to the skin, the only way I can think of (and the thing I did that one time) is to go to the vet and let him shear the fur.
My persian cat had the same problem. It had become pretty serious, so we got his hair trimmed "like a very close shave". Today he is fine and fit. So, just go and get your cat a shave and bath with a shampoo designed to kill the mats. And from there on, everyday, you need to groom him/her until the hair has grown a little and clean ears atleast once in two weeks.
You could try picking the mats apart, starting from the outside, until they can either be combed out or trimmed out.