Found this explanation
Many taxes in Spain are calculated by reference to the “rateable value” (valor catastral) of the property, which is assessed by the Tax Office and revised every 10 years. The valor catastral is generally considerably less than the purchase/sale price of the property.
I bought my property in 2003 and a couple of years later Torrevieja council announced that all Valor Catastral would be rising over a 10 year period. Some properties hadn't had their VC recalculated since they were originally purchased 10 or 20 years previously and there was a huge difference between properties of a similar size and the IBI being received.
So it would appear that you to are being caught up in this gradual rise of VC.
I believe in some areas of Spain the VC has gone up 200 or 300% so I suppose we should be grateful.
As a non-resident I have to use my Valor Catastral to calculate my wealth tax and Property Owner’s Imputed Income Tax (Impuesto Sobre la Renta) . (Wealth Tax has been set to 0%)
From what you have listed Arne it looks like you have paid 2010, I don't think the penalty figure is very large so you could delay going into the Suma office until October/November when it will be less crowded.
I bought a car last year and it has been registered with my plot number rather than my correos number. I therefore didn't receive a car tax reminder so had to go into the Suma office to sort it out. The suma cannot amend my incorrect address so I arranged to pay by Direct Debit for all future years.