If my ex lives in NH and I live in WV, but divorced in GA, what state do I try to do a child support modification?

My ex is active Navy and NH is home state. We divorced in GA where he was stationed. Soon after I moved back to WV and he got stationed in NH. Our daughter is 17 and out son is 20,he is in college. When my son turned 18, my ex said he would leave the child support as is seeing how my son was going to school. Now our daughter will be 18 in July and will be going to college also, but my ex informed me he will not be continuing any child support. Can I get a legal modification for child support? In NH, if a child is in college, the child support continues? Can I get a modification in NH? I am not sure where to turn. I spoke with an attorney in GA and they advised I contact an attorney in NH. IS this what I need to do? Our children have lived with me in WV since 2001 and their Dad is not really in their life. He hasn't seen them for at least 3 years and not very often prior to that. If I can't do a modification, can our daughter take her Dad to court for support while she is in college?