not paid for hours worked

I'm on my second job now where my Japanese employers at companies in Guam will not pay me for the hours I work. At the first job I just talked with the Fed Dept of labor to be sure they must pay me, then I brought that information, respectfully, to the attention of both my supervisors and then to Human Resources. At each of four pay periods, when my supervisors asked me to sign my time sheets which had been altered by them to reduce my time worked, I made notes at the signature saying that the time clock was accurate and asking to be paid for all hours worked. Then I took the issue up with Human Resources. Each time HR assured me that they followed Guam law. After the fourth time I asked to be paid for all the hours I work, they fired me.

Now I'm trying to keep my job working for my current job, but they want me to write down on my time sheet that I always work 3 hours, even if my before and after shift duties make it so that I am working 3.5 or 4 hours. I called the Fed Dept of Labor here in Guam and was told they could do nothing to protect me from being fired. I can complain to them, and they will investigate, but they don't have the power to protect my job if I do.

Surely this happens to others. Is there some way to solve this dilema?