Accounts do not get reset on their own. There are three reasons your account may appear reset:
You deleted your account via the Game Settings/Profile (this is pretty rare)
You are playing on the wrong server
A lot of our games have several game servers - make sure that you try all of them before you panic
You accidentally changed the language
Make sure that you're playing the game in the right language. Our games do not switch languages - each language is hosted on a different server, and if you change the language, you'll begin playing a completely new account. Some of the more bilingual among us might not even notice.
You can find the dropdown to change languages in the top right corner of the screen: