I'm really sick of having hard scratchy towels. I have never used softener on them as that's supposed to stop them from absorbing water and I don't have a dryer so they are either dried inside on a rack or outside on the line. They weren't super cheap, just average.
Try rinsing using washing soda. It removes any excess soap which is what makes your towels hard. Dissolve in hot water.
I'm never without washing soda. I have washed poly filled doonas and they came out looking like new. Because it gets very hot here in Queensland I keep it in the fridge in a small bucket with a tight lid. Washing soda starts to melt at 35 degrees celsius.
You can use it as a rinse for any washing.