回复：虽然我们是外国人，我们同样拥有开心工作的权利！

In terms of SS and Medicare, you can claim it back when you file your tax form. Not every company knows it, no big deal.
You may want to document all your work, use e-mail as a record. ie, job assignment, work load. If necessary, go above your manager to the boss. In a small compnay, typically the big boss/owner cares more about who can get the work done.
Sorry you have the bad experience. However, I disagree
虽然我们是外国人，我们同样拥有开心工作的权利！Because in a work place, it's equal opportunity. It doesn't matter which country we're from, we should be treated the same. It's wrong and illegal to discriminate anyone based on his/her nationality.