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.
All credit cards terms, fees and rates mentioned in this article/post are actual on the posting date. See the current products’ Terms & Conditions on the issuing banks' websites.