Can't log in to account at check out

I can't log in, says username and password are incorrect. I tried resetting my password (even though I know its correct) but it won't let me do that. I try to register again with same email address and I get an error message saying there are technical difficulties. My email address is always lowercase so its not that. I'm frustrated enough that I'm about to go shopping elsewhere online. I've been trying to get on for a few days now.