This means that you have more than one account at FeedBlitz, and one of the others is in an ad-funded grace period. If you look at the suspension email you received, note carefully the email address it was sent it to (e.g. it might be firstname.lastname@example.org instead of email@example.com). Log in with that account and upgrade it or merge it into your upgraded account via My Account | Merge Accounts.
Only publications (updates you make available for others to subscribe to) are affected by suspensions. Your other subscriptions that are sent to that account will not be affected.