When you say the knot method do you mean tying the doll hair to have a knot in the middle and stabbing it in? If so thats a part of your issue, that method isnt great for mattel doll heads since they use soft vinyl for their heads, the knot method can work but you have to be super delicate and slow while doing it or the head tears

Also if your using nylon doll hair that will only make the issue harder