My hair has two large tight knots the size of a fifty cent piece. I have tried EVERY tip that I was able to find on line. Nothing has worked. The only thing I have not tried is a wet brush as I do not have one.
Try soaking the knots wet, like, when you wash the hair, then apply a good amount of conditioner and gently work it through the knots and the area around them. Be careful not to entangle it more. Then gently comb it with a very large-toothed comb. Once it's mostly untangled you can move to a finer toothed comb to finish the job. My hair is VERY prone to get entangled, and it works fine for me.
I also suffer from this issue, having thick, curly hair.
My technique is to spend a long time in the shower with lots of shampoo in my hair. I just work my hair with my hands like a brush for 10-15 minutes, with the shampoo in it. I find this loosens the hair up a lot. I then use conditioner and do the same thing.
I've found that once I'm out of the shower, its very easy to brush.
The way I have always managed to untangle knots in my hair was to take it out from the (bottom) edge and tiny bits at a time.
It helps when you are can see what you are doing, if only in a mirror.
Tease a bit out, with a comb or even the single spike some combs have, or a hair pin if you happen to own one.
Keep teasing bits on the edge, till the whole is so small that the edge you work on is the middle.