This is a well known issue that can be easily fixed. The issue is that you didn't "unlink" your bot of your Facebook page before you deleted your bot or switched it off. In that way the itsalive app cannot send information to Facebook saying you want this feature ON again.
If you want to read more about the feature you activated without accidentally activated go here: http://help.itsalive.io/en/articles/2137276-enabling-users-to-send-a-message
Here are the steps your must follow in order to get this fixed easily.
1 - First login to you itsalive acocunt, if you deleted your itsalive account you must create another free one (using the same email).
2- Go to your bot > Settings > Connect to Facebook (or create a new one) and connect your bot to the Facebook page that you want to unblock.
3- Then go to the "Persistent Menu" section and switch the "Send a message" ON
Voila! Your users can now talk to you again.
Now go back to your "Connect to Facebook" page and unlink the bot from the page if you wish to take it off.
Facebook has a strong cache and it can take some time, if it doesn't work the first time, simply "link your bot" to your page and "unlink your bot". This should do it.