This sounds bitter. You both made choices, and I doubt you'd have preferred being the weekend parent when they were little.
You think out of principle he should have given you money, he thinks out of principle you shouldnt have pursued it.
Youve no idea what if anything he told them. But honestly, reading this post in your words it sounds like youre blaming him for not giving you money you arent entitled to, blaming CMS, everyone but you. And you did have an original post where you considered if starting this was a good idea and it was all for money your kids didnt need.
You need to accept your fault in this, because its more your fault than anyone else's.
You need to let it all go and reach out to the kids, I hope you were able to send them their gifts