Talk to the labor board at the very least and a lawyer if at all possible.

do you have anything written from them saying you're hired? or when you were supposed to start?

Congrats on completing your internship.

Get out now they are just going to keep screwing you over. If you do manage to get them to pay you i can almost guarantee that they will try to find a way to fire you and make it look like it was your fault.

The whole month they didn’t say anything? Is that even legal?

Quit, ASAP!

So they just let random people come in and work without telling them they’re hired? I don’t think so. I’d call the labor board.

If you have a letter or email from them stating that you were hired (never do anything like taking a job offer without it being in writing) then they would very likely be acting fraudulently by not telling you you were not actually hired and taking services from you in respect of your work.

My last 2 jobs were obligated to pay me even if it was something silly like less than 15 minutes off the clock duty and for whatever reason I had to clock out and back in. At my current job if I'm sitting after my shift decompressing and someone asks me a question because I'm still there, I log back in because it's work related. They are obligated to pay you for work related functions, and chances are orientation and training and all that couldn't even begin UNLESS they found your papers to prove you were in fact hired. You shouldn't have been let in the door the first day unless the papers were in order. That's how all my jobs worked out. My current job pulled a few people from new hire training stating "we didn't get your drug test/background check back yet, so we have to get you into the next class", or "there was a problem and we are not hiring you after all." The offer letter was "contingent on passing background checks, previous employment checks, and drug screen." Keep all your time stamps of when you clocked in and left, and if you can take log of what you did at work as job duties, and take them to a lawyer. Oh yeah, and figure out when your probation period ends and health insurance coverage and 401k matches start. The day you started working or the day they got the paperwork straightened out? Also points to bring to the lawyer. And do you want to work for a company this disorganized? It may be a sign not to stay.

in the US, they definitely are obligated to pay you. they knew you were working and they didn't stop you. thus they have to pay you