I accidentally extended my ESO Plus in the PS Store twice... I was charged twice, will that give me two months before it automatically renews or have I just wasted 20 bucks? Anyway I could get a refund?
You won't get a refund, that's for sure. It's in their policies. I'm pretty sure you'll get 2 months for it, you should be able to check when your sub ends on your ESO account (ESO website), just to make sure.
If it doesn't then you have a case, but like I said, they'll probably just make sure you get that second month, they won't refund.
As mentioned, check to see if your ESO+ membership goes for two months or just one. If just one, submit a support ticket to see if you can get the second month that you paid for.