As a contracted employee, how can I ensure that I get paid from my employer who is withholding pay?

I am a contracted employee that is having trouble getting paid for my work. I've worked with a company for over 3 years that owns several separate locations. I am employed at two of their locations however one of them recently laid me off. I set up a gmail account that I used for both locations and another job I work for. When they fired me, they hacked my account and changed all the account holder information and passwords. They are now withholding my pay and telling the owners that it is because I am keeping important clientele emails from them. This email was the only one I used for any of my three jobs and they are jeopardizing my work with the other companies plus not paying me.