1st, yes, if he were a good father he would pay and pay willingly. What good parent would not want their child, regardless of divorce, to have the advantages of being in a financially stable environment? From someone who collects child support I will tell you that child support isn't a thing that is being used to punish the other parent. It is to make sure the children live as well as they would if the parents were together.
2nd, I would NEVER put my child in the middle between myself and his/her father. I would not make my minor child go to his/her father begging for money for this or that. That is manipulative using the kid because you know the other parent will feel guilty. Financial decisions are supposed to be made after a discussion between 2 parents. That shouldn't top just because they are not together.
3rd, the OP did try to get her daughters' father to help physically, rather than monetarily by having the girls spend the night at his home a few nights a week as he lives nearer to the job/camp. He refused. Remember, legally we can make the bio pay, we cannot make them parent.
4th. That money for camp did not go to the OP. It did not benefit the OP, it was for his child. For something that was important to his child and may positively impact his child's future. The OP, in no way (other than having a happy child) benefitted from that money.
I do not have a dog in this race, but I always have an opinion. LOL!
I do not approve of any parent tell a child no to extra's such as camp or sports just because they can or becuase they insist that CS goes for that. I do understand that there are times when a parent simply cannot afford the extra. As a single Mom who did not have an ex to go to, I said no when I needed to. My kids understood that they could not always have what they wanted, even if the want had merit. I gave what I could. Divorce does not change that living expenses sometimes mean that kids don't get all they want. I know that many times children of divorce seem to pay that price more often, and they had no choice in the decision their parents had to make, but two households cost twice what one does.
As children grow up they need to learn how to discuss with adults, even their own parents, how to pitch a proposal. Mine did, as does my DGD. DD has insisted for years she do this with teachers and with her and Dad. DD helps her through the process, but at 14 DGD has learned how to approach an adult with a clearly outlined plan for what she either wants or needs. I see no reason, unless a parent gets nasty, why teens cannot approach a parent if they want to do something "extra". They should be taught to think the entire project though so all angles are covered. In this case, even Mom did not think it through. I am not going to speculate how many times Dad has agreed to pay for something and then gotten hit for additional expenses. I will tell you that I love my kids, but no way would that happen to me more then one time. I had a finite amount of money. If I allocated a certain amount to something but then was told I needed more because my kids, and in this case their parent, did nto consider total cost, and this was not the first time, I would be angry. Sometimes people refuse to consider the entire picture because if they do, the proposal would fail. We call it "cost plus" and I hate it. Give me a cost, and be honest. If you are not, you pay the additional fees. Next time, when it may really count, you will not be so shortsighted.
I have no idea why the father refused to have the girls stay. If my kids were not in my home daily, I would have moved Heaven and Earth to have them. I will say that I would need to know more before I jumped to the conclusion the OP ex was choosing not to parent. I read the entire thread, but perception is everything. I have friends who are divorced, and neither one can see the other's POV. The truth is that somewhere in between both of their peceptions is where the reality lies, but to them? YIKES!
I wish that there was a real way to make people understand that CS is not used for wine and cheese for the custodial parent, but since we all have heard horror stories about abused CS funds, that tale seems to be in place. It is my opinion that many times the non custodial parent wants the other to forego a life that includes some niceties.
It is too late for the OP to make too many changes here, but I will say that this kind of thing is not going to end even when their DD's are over 21. Both are going to need or to want to manage extras for them, and in order to do that they will need to be specific at the get go in terms of who is paying for what and how much each is committing to pay. I figure that this "learning experience" for the OP will make sure that as a family they all become more adept at planning their extra expanses with an eye to the "intangibles" that pop into the picture.