hi there. i hate to tell you this, but once the mats are all the way to the skin, it could be that the only thing to do is have the dog shaved. we just went through this with our labradoodle yesterday!
she had gotten into some (thousands!) burrs, and we tried combing them out but to no avail. turns out she was also so matted that they couldn't get a comb through and in that case they must get rid of the mats. they had to shave her but honestly she doesnt' look nearly as bad as I thought! I was dreading picking her up from the groomer.
see, if you have mats and the dog's hair gets wet, it tightens the mats and they can actually end up pinching the dog's skin which is painful. also, they won't dry properly and you can then get some skin problems and sores.
believe me, we had our dog slightly groomed this summer (much to my husband's chagrin!) and i thought I was keeping up with brushing her, but her fleecy coat is so thick I wasn't getting all the way down to the skin. she had such bad mats by yesterday that it was more of the reason they had to shave her than the burrs were the reason.
the groomer showed me a metal comb that we need to buy for in a few months when her fur starts getting long enough.
i didn't realize this but our dog is considered a "high maintenance" dog in grooming terms because she has more of the fleecy poodle coat than the wiry lab coat. now I'm jealous of the labradoodle owners who have the wiry coated dogs!! but the groomer also said that we may find we end up preferring a shorter cut to the longer wavy one, and we may decide to keep her cut shorter. i doubt my husband will ever agree to that, but I might!! brushing takes a LONG time, and if you don't get all the way down to the skin, it will mat anyway.
i'm so sorry! Take your dog to a good, reputable groomer, and see if they can comb the mats out. do not bathe the dog!
i think what happened to us is that when we took our dog to the doggy day care/kennel, they bathed her and maybe didn't brush her out before and after. because her mats seemed to pop up after the stay at the kennel.
good luck!!
Christine