It took me an entire week and all of the goodwill I’d built up with the cat to get her some relief from that first six months that I did not pay enough attention. In case this has already happened to you, I recommend you take the cat to a groomer. If you can’t, here’s how I approached it.
You want to work on the most painful mats first. Judge by the redness of the cats skin and prioritize the belly, where the skin is more tender. You need the scissors described on the main page for this.
First cut the edges of the fur that are causing the pull against the skin. I use a nibbling motion with the tip of the scissors for this, trimming away at it until the mat is loose enough that you can pull it taut.
Once it is loose, hold the mat out and away from the skin and snip underneath it as close to the skin as you can safely get, until the mat comes away.
Snipping the mat off is not the end of the problem, because you will still have knotted undercoat in the area. For this, you want the comb I show in the main page. Since the skin in this area is now quite tender, you might want to wait a day to pull through the remaining mat.
I removed the mats one at a time, working at the worst ones first to give the cat the most relief. Annie gave me very little time to help her in these first sessions as she conflated the pain from the mats with my ministering to them and kept trying to bite and scratch me to get away. To keep my arms safe, I held her on her back in my lap and had a heavy bath towel over her hind legs, leaving only the mat I was working on exposed. I wore blue nitrile gloves and a long-sleeved tee for the same reason.
Once the mat is clear, tease away at the remaining knotting with the comb. Now that the fur is short, you’ll have better luck with it. Continue to work at all of the mats until they are all relieved, and operating on a worst-case-first basis. You’ll know you have succeeded when you can go through a regular grooming process without any drama.
This clean-up took me a week or more, as Annie’s patience wore thin so quickly. So my advice is to make sure whatever grooming you are doing is actually working before your cat gets in this condition.
Seventy seven years of learning just about to become toast. Throwing it out there.