If you lose your Apple watch and it's connected to your banking app please contact us on 13 25 77 to request that your card be disabled for use with Apple Pay, or log in to the mobile app and block your card using Card controls.
You should also go to iCloud.com and remove your card from Apple Watch. If you find your Apple Watch you can re-add your card back by following the same steps you went through when you first set the card up with Apple Pay.