Thank you for reaching out to the Community and I apologize if it appears a number of contacts are missing from your account. This is not an issue we've seen from other customers and after looking over your account I do not see any history of a large number of contacts being removed around the time your account was migrated. We will need more information to try and troubleshoot and figure out where the contacts may have gone.
1) Are you seeing the loss of contacts reflected in your Active Contacts number or in a particular list?
2) When did you first notice the contacts were missing?
3) Can you provide any example e-mail addresses that should be in the account?
For privacy reasons, feel free to reach out to us at social_support(at)constantcontact(dot)com with your username, a reference to this post, and the example e-mail addresses and we will do our best to resolve this issue for you.