Why do I get paid minimum on my final check when I had put in my 2 weeks notice?

I was making $11/hr and was looking for another job and found a better opportunity with another company. So I put in my 2 weeks notice on paper and gave it to my supervisor. 2-3 days later at work I was feeling horrible and I was trying to find any upper management so I can notify them that I am unable to continue working. NO SUPERVISOR or GM was anywhere to be found so I let me team captain know and he said to just leave and that he will let the supervisor know whenever she returns from wherever she was, so I left. Then an hr later I get a text on my phone say that my assignment with the company has ended because I did not notify my superior. How am I suppose to notify anybody when nobody was around???? So I went to pick up my final check and it was minimum wage. ???????? Are they allowed to do this????? What can I do to receive my full amount and who do I contact???? I was working for a Temp Agency