For a long time, your ex-spouse failed to pay any child support. Now that your child is older, the payments are finally being enforced. Your biggest issue with this is that your child has missed out on years of support from the other parent.
The thing you should know is that you can seek back child support payments. There is no reason why a parent should get away with not making payments just because they didn't want to or didn't seek modifications. Child support is ordered by the courts and must be paid unless other arrangements are made.
Can you seek retroactive child support?
Yes, you can. When you file for a modification or file for child support the first time, you can ask for retroactive support for the times when the other parent didn't pay. You should provide some evidence of your attempts to obtain payments, such as time spent with your attorney or requests filed with the court. If the court is satisfied with the evidence you have, then it can order child support payments be paid retroactively for as long as it takes for your child to be paid in full.
What can you do if the other parent isn't paying?
Discuss your options with your attorney if the other parent is not obeying the child support order. Parents share the responsibility of raising a child, and there is no reason that one parent should shirk that responsibility without a good reason. Children depend on support for many of their needs, so it's important to have the order enforced.