When do I have to repay and what amount from the credit used on the Direct Card?

For BT Direct credit cards, you have a payment period of 25 days.
Check the monthly account statement and pay the amount found in the "current month debt" section by the mentioned due date.
If you encounter difficulties this month, you can pay the minimum amount from the account statement by the due date, with the mention that next month you will have the difference to pay, as well as interest.