Ramondon, I would do this: make a surprise visit to YOUR apartment (if you pay mortgage, I guess you have a title or something similar, right?) and see the living conditions... see how the fridge is stocked. See if there is milk for the child. See the clothes. See and take pictures of everything.
I would do the visit in presence of your attorney and another witness, maybe a religious minister.
If at any point you feel that the US$400 you send is going where it should not go, you can go to tribunal de menores (you can visit fiscal de menores for that over there in ST, also you can go directly to SD to La Feria and make appointment with Marisol Tobal in Procuraduria General, Jueza de menores, the very boss. She is VERY good at having the laws enforced and helping the struggling parent ---regardless of sex -- against the abusing one).
In the Tribunal you ask that the child support be changed from "cash support" to "material support and some cash" ... so you can, for example, send only US$ 100 to US$150 a month and pay the rest in food, clothing, medical insurance etc. You would make arrangements with a local supermarket who would send a monthly food basket (canasta mensual) according to the nutritious needs of the child, not the mother and chulo.