The time that took you to post here, could have been used to "google" for the bank info.

Contact your bank immediately...procedures may vary from bank to bank, but in general is:

* call the bank
* raise the issue of lost ATM card
* ask to block/cancel the card
* ask for issuance of new card/pin code

By the way here's the link to the bank info

http://www.arabbank.com.qa/en/waysbankbranchnet.aspx?CityID=55

Regards!!