Sorry to hear that this happened to you. When an order of child support is in place, generally there are state law provisions that allow you to move the Court to modify the order when the circumstances of the non-moving party (here, your ex) have changed such that it is no longer just and equitable that the previous order continue to be the order. This is called a support modification.
You might want to look for an attorney that is a little bit more confident with their litigation skills. Every state has civil rules that provide that each party can ask the other party questions about their income, expenses, liabilities, assets, etc. This is relevant to the issue at hand (e.g. whether the support order is correct or incorretly set) and necessary. Courts can award a requesting party attorney fees, especially when the party whose information is sought is clearly evading the truth. There are forensic accountants who earn a good living doing nothing but ferreting out assets that people don't want to show the Court. KY may also have a way for you to request post secondary (college) support for your boy. Car insurance is a huge expense when teens are added to your policy ( as you know well).
You can get certified copies of the KY order exemplified to SC and pursue the matter on your home grounds, as you and the child live there. The better organized your financial records are, the easier this is going to be.
But don't think of this as a hopeless case. It isn't. But if he's being that difficult, don't share your thoughts or requests with your ex, lawyer up and have at it. Also, get references and really seek out an attorney who understands this problem and is prepared to do the discovery to get the answers you need.
Hope this helps. XXXXX XXXXX