Do you still have services? If yes, this could be your account going through the normal renewal process. The SELF SERVE account can say "expired" or "suspended" on the day of or before your plan is due to renew. So if this is the case, ignore these messages on your SELF SERVE account.
If you have no services, and it is past your renewal, maybe your autopay failed?
Add Funds to your Plan Amount through SELF SERVE (or by calling 611 if you have a card registered)
Go to “Plan and Add-Ons” TAB
Select "Lost/Stolen Phone" TAB
Select "Suspend Service" BUTTON
Then, Select Resume/Reactivate Service
Reboot your phone.
If this was an Autopay failure, I would let the Customer Support Agents (CSA) know.
And, also ensure all rewards were or will be provided to you.