If you're unable to find your licence reference number, you can use the 'driver licence (badge) look up' feature available on the renewal application page. Simply enter your name as it appears on your paper licence along with your badge number in the format PHD123 or HPD123. If this does not work, double-check your paper licence for discrepancies in how your name is recorded.
For more details on renewing your taxi driver licence, you can visit the application page.