Hi I also noticed that I got a bill a month after my last one. What I did spot though is that I think they have switched to using the data from our newly fitted smart meters (remember the power outages early this year to fit them). Unfortunately our apartment was empty for the billed period so there was no usage data.
http://www.iberdroladistribucionelectrica.com/consumidor
I did try to register for the access to the smart meter data, it is a different site, but as part of registration they need to send a text to a Spanish numbered mobile. The field won't accept uk mobiles. When I raised the issue with Iberdola they confirmed that it must be a Spanish number!
So not much use to most of us.
Jim