There are several reasons for this, but first look at its status in your BtcPremium account.
If the status of the transaction is "Pending" then it is likely waiting for approval of the administrators. (3-5 times daily Monday to Friday)
However, if the status of the transaction is "approved" and it's been 24 hours since the request was submitted, open a request at our support portal, and don't forget to mark the TXR number of the transaction.
We can not investigate any request in the first 24 hours of the transaction.