If they continue to list you as part of the sex registry, it is likely that they believe there is a reason to do so. However, the DPS (like any agency) can make mistakes from time to time. As a former DPS attorney who now crosses swords with them from time to time, I have found the DPS to be straightforward regarding its management of the sex offender registry. That doesn't mean they do it right, it just means they will explain to you why they are doing what they are doing.
Your question does not give enough information to allow me to provide direction. Some questions you might want to answer are:
1) Do you know why the DPS has you on the registry?
2) Have you attempted to explain to them in writing why you believe you should not be on the registry? How many times? When? Do you have the names of the people you spoke to or wrote to?
3) How long has this been going on?
One thing to remember is that time and money spent on an attorney to fix the problem is generally not recoverable because the State of Texas and its agencies enjoy sovereign immunity from suit.