Child support adjustment?

Been married for 7 years husband has a child from previous marriage child support has been 200 a month the whole time but in those 7 years we have had two more kids with one on the way the mother used to send her kids for weeks at a time before he started school but Noe that he is older she is constantly changing or not sending him for visitation but we still have to keep up payments. Should there be an adjustment in support now that we have so many kids of our own it doesn't seem fair that we have to pay and she doesn't have to send him on court ordered days. We live in mississippi