We have not been getting charged in the past but we received an email stating we need to upgrade.

We are going to be limiting the number of forms each level of subscription is allowed to create.  Free accounts will be able to have a maximum of 5 forms.  If your account is currently over that number, you simply won't be able to create new forms. 

If you need more forms than your currently have, you would need to upgrade to Silver or higher.