If you lost you credit card, the first and immediate step of yours should be contacting your bank as soon as possible (better calling), and inform them about it. They will close this account of yours or freeze it, so no one will be able to use this card.
The bank will charge you for the lost credit card, and if you express an intention to continue using this type of credit card, they will assign a new number to your account and give you another credit card.
But you should act quickly, as your card could already found and made use of.
Disclaimer: This editorial content is not provided or commissioned by the credit card issuer(s). Opinions expressed here are the author's alone, not those of the credit card issuer(s), and have not been reviewed, approved or otherwise endorsed by the credit card issuer(s). Reasonable efforts are made to present accurate information, however all information is presented without warranty. Consult a card's issuing bank for the terms & conditions.
All rates and fees, and other terms and conditions of the products mentioned in this article/post are actual as of the last update date but are subject to change. See the current products' Terms & Conditions on the issuing banks' websites.