There have been SOME cases of people hacking into sellers' Amazon account, re-routing the sellers funds to banks in different countries (yikes!) and more.
There are some almost fool-proof ways prevent this from happening to you:
1.) Change your password to a strong one (tips here) and, more importantly:
What does 'two-step verifcation' mean? In short: you have an option to ensure that you (or anyone) who wants to log into your Amazon Seller Account - with your username and password - has to verify "it's really you" by receiving (say) a mobile text msg or phone call or email, for each log-in attempt.