What can I do if I was wrongly accused of fraud and was denied my last paycheck?

I was working at a bar and, by the time I was hired, my manager said that I would always work 6 shifts of 6hrs each, always on the same days and time. Hours were ok, but I complained about the money and he said I could sign two hours more per check (checks were weekly). So, I would work 6x6=36 hours a week and would sign up for 38. He told me, since my hours would always be the same, that I should always sign for 38 hours and have it as it was a salary (even though, technically, it was not). When there was an exception and I had to work more hours to cover the other employee, (hence there was just 2 employees) those extra hours would be added to my paycheck based on the 38 (ex: if I had two extra hours to receive, I would get paid 40 hrs. this would be authorized, verbally, by the manager). Here is what happened: After 2 years working on that place, having 4 checks a month with the same value, or with added hours having the 38 as a base, the owner decided to look at the payroll. Now I realized that the manager had not reported this deal to the owner. As a result, I was fired and accused to add the 2 extra hours without nobody authorizing it. The manager is probably afraid of suffering retaliation and is denying the whole story. Plus: the owner does not want to give me my last check. What is the best way to proceed? Can I sue them or the manager? How can I claim my last paycheck?