Deadbeat (venting)

My oldest daughters dad is $5000 behind on his child support....in the beginning I tried to be able understanding. I figured maybe he was having a hard time or an unexpected expense came up but now it's been months since he's even attempted to make any sort of payment. I have talked to him about it and he always tells me he's sending a payment...but never does. Last weeks I contacted him because our daughter had to go to the hospital so I was letting him know what was going on with her and he told me that he was sending it in and it would be almost caught up. I was like awesome because she is due for her eye exam and will need new glasses and school is starting back up so it will help a lot. Fast forward to now and nothing was sent. In fact he is on vacation right now and just bought a car (a hobby of his, not a daily driver).....I text him asking what happened to the payment and he never responded. I'm so fed up....I'm so tired of being lied to. I've asked him to just be honest w me so I know what's going on and know how to budget but he still lies. Lord, I just wish I could go off on him. I wish our daughter understood what was going on, but I try not to let her know bc it's not her problem to bare. I just don't understand how you can not give a flying fuck about your kid.