I'm sorry for any frustrations with your email campaign! We'd like to look into this for you. Can you please send us an email at social_support(at)constantcontact(dot)com along with your username, a reference to this post, and a few more details such as the name of the email campaign, and an example of a contact who received your email campaign more than once? That will greatly help us in troubleshooting this for you!
As far as the Social Share area you can remove an individual post by clicking on "Remove Post":
I am so sorry to hear that! Did you receive any kind of error message when trying to remove the post. When you scheduled the post, was it already published on social media? If so, you can go on Facebook and delete the post. To do so, take a look at this article. If the post was scheduled for a different date/ time, you should be able to go into Constant Contact, remove the post, and select "Save Changes" to ensure the post won't go out. Please let us know if you have any other questions.