What is the legal process for child support revisions?

i already have a child support order in place, however, i requested a review to revise the order to increase the amount of child support i recieve.(due to the fact that the original amount was based on minimum wage because he wasn't working and he now is, so there was a substantial change of income which merits the revision) The father did not attend the meeting and a new order was written but they told me it is called a "non agreed order" and that they would have to serve him this new order and give him time (20 days) to dispute it. They have been trying to serve him for about a month or two now and have been unsuccessful. i know he is intentionally avoiding being served.(ie he just won't answer the door.) Is there something i can do to speed up this process? is there a certain amount of time allowed by law for him to be served? what happens if they cant get him to open the door to serve him? i would appreciate any advice you can give me as im sure you can understand my frustration with this issue! many thanks! by the way i live in texas!!