Do I Work For Bad People Or Am I Not Smart?

I am a manager of a successful sports bar/night club. I have been at the establishment for 17 years, working my way up from bartender to general manager. A few years ago ownership changed and I “came with the frame”. Since I know the building and how everything works I now run the place, and I do a really good job at doing it.

That said:

I was doing inventory Monday afternoon and a person from “corporate” (it’s an extent to say that) came in to make sure that the safe count I did was correct, as they do once a week. I wished them a happy holiday season and when I finished up I went to clock out and past days on our program were on the screen and my hours were WAY off from when I was working.

I am hourly, my normal shifts are 5-4:30. They changed my hours to. 7-3 with a 45 minute break that I never take, saying that “we just thought you forgot to clock out”. (Our system automatically clocks us out at 4am if that helps)

I went back and looked at many old paychecks and I noticed that, even though I’m punctual, I’m not as punctual as I am clocked in for. I have multiple checks where my “hours worked” ends with “x.00” no one can clock out that fast.

With my hourly, I feel like I’m owed tens of thousands of dollars but I don’t know how to prove it.

I can prove the last check for sure, but looking at previous checks it might be harder.

What should I do?