回复：Help!在线等。。绿卡已经收到了，还需要再去按手印么？？谢！

I experienced exactly the same.

I called USCIS and the officer told me that I had to show up in the Support Center and the officer there would tell me whether to have biometrics taken or not.

Two days later, I called again and spoke to a different officer. And she told me ignore the biometirc appointment. So I returned the biometrics appointment letter along with a letter stating the situation and the officer's ID and her instruction.

I have heard nothing from them ever since.

Good luck.