Which may be why they can't take them by phone (if the centre is based in Germany). Maestro is a PITA in banking terms, a brand name that's been slapped on a hodge podge of different national debit systems by banks (many of which are in the process of phasing them out)

Take for example websites that take UK Maestro (formerly known as Switch) - they couldn't accept Irish Maestro (which is basically an altogether different national debit card system), and couldn't take a German issued Maestro etc. Use internationally is also an issue. I do wonder if their physical location (Germany) precludes them from processing Spanish issued Maestro cards there over the phone.

I don't know if the suggestion is unwelcoming as such - to me, if it's a problem they can't solve (and it may well be impossible for the agent to resolve) - they've made as solid a suggestion as they can do, given the circumstances.