Has anyone ever managed to get an invoice/factura from Iberia Express?

I have my first flight for business reasons with them comming up this week. Their IT is bad enough to make IB mainline look good.

Their FAQs say to ask for an invoice from the booking management on the website. It's a new route (CDG-MAD), and since I bought the flight, they have changed the schedule several times. Every time I tried to manage the booking, it asked me to accept the changes then froze. I eventually managed to get the booking centre to fix this when I called them (on the third attempt), it only allows me to set the frequent flyer program/number, and does not allow me to ask for an invoice.

If I call Iberia Express, I get one of these answers:

• We only issue invoices for flights that start in Spain (?! that can't be right)
• They transfer me to ServiIberia, who then tell me they have nothing to do with Iberia Express flights
• They tell me to wait until after I have flown and then to check. This feels like a fob off, and I'm worried that I won't be able to see the reservation once I have flown. But then Vueling only issue invoices after the flight has been flown (which is a good reason for not flying with them as I often book flights up to 6 months in advance).

Has anyone successfully got an invoice from them?