You can remove your payment method at any time via the customer portal.

Please follow these steps:

1. Log in to the customer portal via the following link: customer portal.

2. In the customer portal, select the "Payment method" section, on the left. 

3. Click on "Remove Payment method".

5. Voilà! Your method has now been removed from the customer account.

Note: Your payment method cannot be removed if you still have open charges for value-added services that you have used in the current period.  

See: What are value-added services?