I currently am on FMLA-Michigan- and am paid 100% of my pay. I received a call from Human Resources but missed the call. But since I have talked to some people from work I have heard that my current position has been re-assigned to different people and it will not be there when I get back. Can they legally do this while on paid FMLA and do they have to continue to pay me my salary until the doctor releases me to return back to work?

They must return you to the same or comparable position when you return with only a few exceptions. You can read about FMLA at: http://www.dol.gov/esa/regs/compliance/whd/whdfs28.htm