OP, you need to let go of whatever has gone on in the past. You feel wronged about how he has been able to build his career, but that isn't going to help you get what you want in the future. You have to let it go.
I assume the goal is to try to get back to regular contact with your children.
Pay the maintenance, teenage children fully understand about money, and it will not help your relationship if you have to be forced to pay your share of their costs.
Once you're paying regularly, and the heat has been removed from this situation, reach out to your ex and ask him to facilitate regular contact.
From my situation, I didn't receive a penny in maintenance for years, worked full time, was always shattered, but have 2 daughters who want nothing to do with the father who refused to pay and made everything about money. 19 & 23 they are now, and I honestly believe they'll never speak to him again. It's not good for children to be estranged from a parent, no one wins. Don't be that parent. Let it go, it's really not worth it.