I'm not sure what the "typical" expectations are for work/stay or internship scenarios, but to me that sounds pretty unbalanced. It makes me wonder though if there were clearly outlined expectations to begin with, and if so do they match your experience of time spent working and what you're being asked to do. I once had an internship (not farming related) that specified by contract that I was to do 12-15 hours of specified work per week, and they had me doing close to 35 hours of work that wasn't in the contract. That clearly didn't work, and I ended up having to leave as a result of not getting my contractually based req's met.
If you want to stay, I would agree that writing a clear and kindly worded letter about your experience would be valuable. I would recommend also figuring out what you are and aren't willing to do, and for what, and ask to have a sit down to re-negotiate the terms of your stay.
I'm a new farmer and just hosted 5 interns, all with pretty unpleasant results, but all I asked was 15 hours of labor per week in exchange for housing and staple foods. I think part of the problem was that as a newbie I didn't know much about hosting and failed to communicate specifically enough and give them clear enough messages and boundaries. It would have helped me streamline the process if I had feedback from them, and resulted in less annoyance and resentment of them, which probably came through as a result of my frustration. They might similarly not be aware of things they're doing wrong, and it would be good to figure out if they don't know and care, or know and don't care.
That being said, I had the most trouble (closely followed by excessive substance use) with getting any of the interns to actually complete the 15 hours, so by comparison, your possibly 50 hours (guessing) per week sounds like a lot if you're not really getting a heck of a lot out of it. If you're one of (by my perception) the few people willing to put in massive hours of work as an intern I'm certain you can find a better arrangement elsewhere. But it sounds like either you need more of a contract up front backed up by the willingness to say no to things that aren't on that contract if someone asks. Easier said than done at first, but it gets easier