I think that you are going to have to wait until the customs release it, if they do.
You don't say how long it has been stuck in customs. It can take a while.
I have always advocated that returning a watch to China for repair is not something I personally would do. I much prefer to spend out a little more to get it sorted with a good watch repairer than risk everything by sending it back.
I hope that you get a resolution to this and it might be worth sending a PM to one of the Mods to see if anything can be done.
The problem you have is that it is not the TD that is causing the problem but the Chinese customs.