My Facebook got Hacked.


I log onto FB the other day with tons of notifications: people from groups and some friends reacting to an ad my account posted on every group I'm a part of. That's to say, a lot. Spent the afternoon apologizing and removing each one. Problem is: Facebook has restricted my ability to post on any group til next week, and some groups have banned me, some have banned my IP altogether... :confused:

They're sports groups, where I usually post my YouTube videos, which are very appreciated by all. I think one of my YouTube competitors is behind this and probably hired some hacker to do that to me, in order to silence me.
MY QUESTION IS THIS: I changed my password to sth a lot more complex, but that's all FB suggested I'd do for security. These hackers can hack into an account without the password, can't they ? Or at least, they can make an account post stuff for them, w/o entering the account necessarily I believe. How can I be sure this won't happen again ? What are my options ? If they make me post the same crappy Samsung message with tons of smileys for a second time, I'm in trouble with these groups (big part of my audience).
Thanks !