If you’ve previously payed for boosters or gold bars, you automatically lose the option for ad boosts. I believe that if you wait long enough (and don’t buy anything else) you will be able to use the ads again. It’s frustrating!
I sadly don’t believe there is any way to merge two accounts. You may be able to make an account with the same email/username as your Facebook account, and connect them then, but I’m not 100% on that. That’s really frustrating, I’m sorry!