I've gotten several questions regarding this issue lately, and wanted to put up a helpful sticky.
When you upgrade, the system does NOT charge the subscription fee immediately. It charges the next morning. If you upgrade and then find that the next morning that you are Premium or VIP, the most common cause is that the payment was declined. This can also happen after an expected monthly payment.
Failed payments can be caused by any number of things. Expired credit cards, insufficient funds, even your bank or credit card company can simply decline for any number of reasons. Sometimes card companies do upgrade security without notifying the card holders, which can affect payments to Turbine.
You can see if a failed payment (regardless of the cause) is the reason on the Account Management website. If the account is changed to Premium due to a failed payment, there will be a red warning at the top of the page noting that "One or more of your subscriptions has been suspended due to failed payment." If this is the case, simply add your new card information, and then click the "Get Unlimited Access" button on your DDO subscription.
If that is not the case (which is VERY rare) then please contact the Account Management department.
Please note that we cannot assist with this issue via the forums.
Please note that the previous issue that cause players who canceled VIP and downgraded to Free has been resolved. And this issue never cause anyone have VIP canceled without a cancellation request via the website or contacting Accounts.
Please also note that the issue that caused players to be downgraded last weekend (4/10-11) was due to a specific issue that has been fixed.