Got fired from Walmart my story

There was a 20 dollar bill in the change dispenser at self checkout I looked around nobody was around and it was early in the morning so I used it to pay for my groceries they fired me for what they said was stealing which I think is bs then a ap guy sat me down alone even though I’m a minor and screamed at me to sign papers and threatened me with the law this was in Dunlap tn they waited a few months after the incident to fire me