Husbands child support legal aid help in Texas.

My husband been paying chid support and paying more than he should when the court ordered child support in 2014 he had better paying job that only last three months.he was paying only 200 a month....now raised it to 400 a month..they still basing it on salary in 2014..anyone in this situation? What did you do ? We trying get legal aid help, anyone dealt with legal aid.. We both work. I have two kid's and we ttc one together.