This might sound dumb but it is a rookie mistake that many make, are you sure you registered your account on the US version of the game? If you look on the game page, there are often several flags.When one decides to register an account it usually makes it, but on the European English servers, not the US English version. Double check which page you registered your account to and check which version you are running the game on.
Tip: When you open the client at the bottom where it says "Region/Language" make sure to select "enus" and not "eneu". If this doesn't work, maybe you should post a little bit more information or contact Support as soon as you can, maybe they can help.
Welcome
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Edit: Now that I think about it, maybe you registered your account on the US version (hence the reason you are posting on this forums) but when you open the client maybe you're running the European version. Good Luck.