Originally Posted by Majuki

Say this: Si hay opción, pulse el botón por euros.

For the transaction that has already occurred, I would do a chargeback. Was there a signature slip?

I also find DCC at ATMs less objectionable since there I've never had a forced DCC situation with an ATM. The ATM might have multiple prompts implying that the sky is falling if you don't accept DCC, but I've always been able to opt out.