Hi owenmroz,
Sometimes when you renew your plan it fails to update the balance right away, or if you do it early it will fail to collect for the renewal.
You can visit any Company Owned Retail store and they will be able to force your plan though for you.
Additionally you can send a Private Message to ATTCustomerCare is part of the AT&T customer service team, They may be able to resolve your Issue. You can expect a reply via return PM(Blue envelope top right of screen) between the hours of 7am-10pm CST Monday - Friday, should hear back within 2 to 3 business days.