This sounds like a problem in your friend’s contact list or address book. To sort it out, first we need to understand where email names come from.
If you’ve been hacked… you’ve been hacked. That means the hacker had access to everything on your computer or in (and linked to) your email account. In either case, you need to review your security.
With email account hacking on the rise, it’s important to understand what it takes to keep your account (and its address book) safe from compromise.