If you receive advertising emails from your own address

The sender address shown in the common mail clients is nothing other than the “From:” header. This header is a text string, and therefore every user can enter any characters, even your own email address, without actually using it.
Therefore no one has stolen the password from your account and no one has entered in our servers: they have simply entered, as the sender, your email address so to deceive you. For further details concerning this we advise you to read “How to identify the real message sender