[petargyurov]

Perhaps your card info has been stolen and someone is using it for their Google Cloud account.

As a sanity check, do you use other Google services (Drive, Photos)?

I think cancelling your card is the safest bet; I highly doubt GC will immediately terminate your account just because of a failed transaction. After all, failed txs happen all the time. You will probably receive an email to update your card info.

EDIT: I guess the worry is in doing the chargeback - might be best to cancel first, add a new card to your account and then chargeback? Not sure...