i want to change my billing date but theres no option

Hi @Emma Diston 

Please see the following steps;

1. Go to ‘Billing’. On the ‘Manage my Direct Debit’ panel, click ‘Manage my details’ and then ‘Change my Direct Debit payment date.’
2. Choose a new day of the month from the drop-down menu (please note: some dates may by unavailable).*
3. Confirm that you’d like to make this change.

https://www.idmobile.co.uk/directdebit

Tom