If you suspect one of your Yordex cards has been used fraudulently you can block the card instantly using either the Yordex web or mobile app. All cardholders have permission to block their respective cards with immediate effect, so if you notice any suspicious activity you can act right away.
Once the card is blocked all activity is temporarily suspended. See this article on how to block cards.
Whilst the card is blocked you should contact the merchant involved in the suspicious transaction in order to confirm it was indeed fraudulent use, in which case you can enquire into recovering the funds with the merchant.
If you believe the details of the blocked card are permanently compromised after checking with the merchant the card should be cancelled and a new card reinstated, whether it be a physical or virtual card.