What are my rights in Germany (Essen)

I have been living in Germany for the past two months. Im no longer working and I understand Im entitled to receiving some of my taxes back and in order to this I need the yellow tax card my employer took from me along with the fact they only paid me half of my earnings how do i claim and whom do i contact to know my worker rights. As wel my living arrangements are part of the organiyation I was workign for how long can i stay there