What should I do to defend my right as an employee?

I have been working for a private held company of 50 employees for almost a year now. Since there are some practices they do which are against my integrity, such as changing quality control data to deceive customers, I decided to call it quits. My last day of employment will be about a week from now. Apparently, they don’t only deceive customers, they deceive their employees too, especially the ones who are not part of the boss’ big family. They did not pay the salary for my first two weeks of employment here and just recently, they wanted to take my laptop before I quit. They claimed my laptop as their property. I believe that this is unfair because in the beginning of my employment, the boss already said that I did not have to surrender my laptop at the end of my employment because it would be mine. Additionally, I also paid half of the laptop and installed some of expensive software like MS Access. When I demanded a written policy about this issue, they could not give me one. What should I do to defend my right? They argued that I am the one who is being dishonest because I work here only for a year. My main concern here is not money because they are willing to reimburse the money I spent on software and half of the laptop. I just feel that they are very deceitful and being unfair to their employees.