Call the bank and cancel the card. It's the only way to prevent it from being used, since any merchant with whom you've previously used the card, or anyone who otherwise already has the card data (including simply a photograph of the card) could theoretically run it in a card-not-present transaction.
Once you cancel the card, the physical plastic card is relatively useless.
But if you want the most certain way to destroy a card, then the only way that is 100% effective and guaranteed to be absolutely irreversible is burning/melting it.