There are several issues in your case. First of all, you may be barred from collecting child support in arreage due to the 7 years lapse. You may have waited too long to collect and your claim may be barred by defense of laches.
Second, if you have a support order, file a contempt charge in the original court. You need to serve your ex internationally, which is tricky. If your ex shows up, great, you would be held contempt until he pays up. If not, the court would issue a warrant for his arrest.
Problem is, it is really hard to collect child support in China. China is a signatory member of Hague convention for child custody but not child support. To enforce a court order in China is difficult, especially there is no reciprocating agreement between US and China on child support. You may try an apostille but it may not have any effect at all. If your ex has any asset in the US, you can get hold of that asset. If he comes back to the US, he may have to pay up arreage before getting a visa or renewing his US passport, if any. Anyways your options are very limited.
You may file for 100% custody or child abandonment/neglect but sounds like your ex does not care anyway.
The other way is to find an attorney in China who is specialized in interntional law and family law to help you. I just had a client who is fighting for custody in Mongolia, which is also a non-member of Hague convention. It is a cooperation of an attorney in the US and an attorney in Mongolia, both specilizing in interntional custody law, to help him fight for custody of his children, who are currently residing in Mongolia. It is extremely difficult.
