I'm 30 and have never had a credit card. What should I do?
Yup. Specifically, get a points rewards card so you get paid for using it.
Amazon's gives you 5% back on purchases there, for instance.
Probably won't get a rewards card with no credit history.
I work in banking and I'll tell you what I tell everyone who is new to credit: Use it for needs and pay it off every month. If you're just looking to establish some credit maybe use it for gas or groceries and pay it off. Make sure you don't exceed 50% of your limit, that'll knock your score down quick, but simply paying enough to drop it below 50% picks it up.
As for the OP, it sucks that they closed them on you, but even still you should be fine. 800+ is a very high score and I imagine you have a long history of credit to your name so it shouldn't hurt you much, if at all. Even if your score dips below 800 it shouldn't impact future loans/cards or the rates. A score in the high 700s is still excellent.
EDIT: I would be upset about losing the large limit, though. Not just for the ratios, but also because it's nice to know you have a cushion in case an emergency crops up. I have an older credit card that I rarely use, I just have a monthly subscription tied to it and pay it every month just to prevent the card from being closed.
I know nothing about credit and using a credit card, I just pay mine off when I have to. The idea that closing a card effects your score negatively is strange to me.
You can close, or have cards, closed. The issue is your first card is the start of your credit history. Once it falls off your report it looks like you didn't start establishing credit until the next oldest one was opened. The rule of thumb is you should never close your first card. It won't make a huge difference if you've been using credit for other things. Like Credit Cards, Auto Loans, Mortgages, etc.