I have a cat whose matting problem has become deplorable, and did so over a series of months. But she turns into a hissing, clawing, biting bundle of fury if you bring a trimmer anywhere around her. It's weird because she isn't a longhaired cat (but is a calico with pretty dense fur). Anyway the sound causes her to go completely insane.
This is the hissiest, most semi-feral, violent cat I've ever had.
Finally got a dematting thing from Amazon, with a 9-prong dematting brush on one side and a 15-prong smoothing one on the other side. She was skeptical at first, and it took about three hour long sessions even to get a little bit of it off, but once she realized it was actually removing the mats, she absolutely loves it and insists on it, loudly purring the whole time (until eventually getting annoyed and hissing).
On the fourth session, finally large chunks of this crap started coming off. Now my floor is covered in balls of cat fur. There's still plenty more to do but at least an end is in sight to this furball nightmare.