Hopefully the groomers we have on here will pop in! I can try texting ours, lol. If you haven't already, I'd put de-tangler on it and start to work a little at a time with a slicker and a metal comb. ETA: Macky once matted her pretty spaniel ears so badly with tiny burrs that I really thought I was going to have the cut the hair, but little by little I got it out this way, and her ear hair was spared.
I'm sure there are other tricks that groomers can share!