No, I'm not being sarcastic (or scartiscatic, either). (Me? Sarcastic. Never.
) You must be 18 to enter into a legally binding contract. Someone under 18 can sign anything they want and the other party can not enforce it. If you're underage, you could promise to pay me $10,000,000 and get me a date with Sandra Bullock - and I couldn't enforce it.
Now, it's possible that your parents signed the contract and agreed to pay - in which case you should be reimbursing them as you receive the money from your ex. Or, perhaps, the hospital has agreed to let you pay, but if you stop paying, they may have an agreement requiring your parents to pay at that time. But if the contract with the hospital was in your name, it might not be enforceable. Take it to an attorney for evaluation.
Then what you can do is subpoena the company's records. Ask the court to order the company to turn over the pay records. Or you can ask the judge to order him to comply at your next hearing. Threats of jail time sometimes accomplish miracles.
Also, ask that the increase in child support (if any) be made retroactive to the date you filed for child support. So his delays will buy him some time, but he may eventually have to reimburse you for all the time of his delays.