If you already have an existing account with an active or deactivated UNDO number, you can easily add additional SIM cards to your account:

• in the application: at “YOUR RATE” next to your UNDO number, you can slide the frame to the left and click on “Request extra SIM card”.
• in “My account” (https://wsc.undo.be/): to the right of “MY RATE” and your UNDO number you can click on “ORDER” to order an additional SIM card.
  Please note: to order an additional SIM card, you must ensure that all your bills have been paid.