If I worked for a company without filling out application, does that give them the right to not pay me?

I was hired thru a family members friend and was just told to meet Monday at McDonald's to ride with them to work. I worked 3 days and was sent home on the 3rd due to not enough work. I was fired later that evening via text message and they wouldn't give a reason. I heard thru family that it was because I was on my cell phone or something. Via text the boss also told me I would get a personal check for working on Friday. Friday came and he's telling me he don't have to pay me because I never filled out an application. I have proof on my cell phone where he fired me and told me I would get paid Fri. I told him on phone that what they were doing was wrong and if he wouldn't pay, I was going to seek legal advice. He then offered for me to start back working with them on Monday. Is what he's doing wrong?