If you live in London:
You can get a refund on your monthly Oyster Travelcard if you lose it. In order to do so, make sure you are registered. Often the easiest way is to apply for the oyster card online and you get registered automatically. Or just fill up the form at one of the tube stations.
Being registered also means you can cancel the card so that no one can use it. Simply go to the nearest tube station and they will sort it out for you. Or just ring the oyster customer service centre on 0845 330 9876 (08:00-20:00 seven days a week). You can also find detailed information on the oyster card website.
