3. I can't get a refund on the bill I paid--it was a mistake only from my point of view, since I hadn't meant to pay the entire thing (over $500), but I pushed the wrong button--or rather, I interpreted the button labelled "make a payment" as meaning that I would be taken to a page where I would be able to indicate the amount I wanted to pay, whereas it meant only "pay the amount indicated at the top of the page."
The fact that it was your mistake doesn't necessarily mean you can't fix it. You may be able to log in, view your recent payments, and click on "change/cancel" next to the $500 one to change the amount. Worth checking. Also, you could call the creditor and ask to change it.
6. I have lived in this place for over a year and have seen three people evicted with only a day's notice.
Leaving a day after your landlord tells you to leave isn't the same as being legally evicted. If you stay put when the landlord tells you to leave, the landlord may--assuming that rooming houses work like apartments, which I'm betting they do in at least some respects--have to legally evict you, which takes a while. Once a person becomes a tenant you can't just kick them out with little or no notice--even if they're living in your house. Of course, if the landlord is evil they might go into your room when you're not there and put your stuff on the street--and that is definitely illegal, FWIW. Might be worth contacting your local free legal services organization (sometimes called Neighborhood Legal Services or something like that). Your county bar association should be able to point you to it. They do a lot of landlord-tenant work. The point of contacting them would be just to learn what your rights are.