When signing up for multiple servers you must use a new/different Paypal email address. The email address is how we track your subscription(s) and can be difficult if created under the same account. You may sign up with the same username, but the email has to be separate from the first account.
You can easily solve this problem even if you have incorrectly signed up for multiple servers.
FIRST: go into your Paypal account and cancel one of your "recurring payments".
SECOND: create a new Paypal email address and use it to sign up for a seperate server.
Warning! To upgrade (or add more slots to your current server) is a different process. In that case, you would use the same Paypal email as the server you want upgraded.