Do creditcards/debit cards/ bank cards get damaged when in contact with magnets?

Old fashioned cards have a magnetic stripe, and it is well known that magnets will wipe out information on these. It doesn't always happen after one exposure. It may take several exposures for the card to be deactivated, but it will happen eventually.

More modern cards that use a chip and PIN system are not vulnerable to damage by magnets.

Depends where you use them.