Originally Posted by Prism99
Try scratching the knot and the fabric near the knot with a fingernail while you are pulling on the thread. Scratching helps the fabric fibers separate to allow the knot to go through.
Are you using batik fabrics, by any chance? They are more tightly woven than regular quilting cottons and therefore harder to quilt.
I do the same thing and if it is batik it is harder.
I also don't cut off the tail. I was taught to put your needle right under the fabric where the knot was pulled through and kind of circle it under the tail and it will pull the tail right under. I hope this makes sense.