How can my child support be raised if no one has served me with papers or anything?

The law generally requires a party to a lawsuit to be served with notice in person.  Most people think service involves you being handed a set of legal papers by a process server... which is the most traditional form of service.  However, the State of Texas does provide for other means of service.  One alternate means is by "publication."  If your ex could demonstrate that you were avoiding service or that she had made diligent efforts to serve you, then she could ask the court for permission to post your citation in the newspaper-- they usually show up somewhere behind the garage sale ads under "legal notices."  The second type of service is on counsel.  This occurs where a party is represented by an attorney and they send notice of the modification to that attorney.  Some attorneys are diligent in responding, but some take the position that they were just hired on the underlying divorce, they are no longer on the case and bail without filing an answer.  To see exactly what kind of service your ex used, you can go to the district clerk and ask to see your file.  From there, you may be able to get a new hearing if you did not have proper notice or if you attorney failed to answer for you.  A family law attorney can also help you with modifying your support obligation and uncovering the type of service utilized in your case.