I had a similar problem a couple of years ago.

They never read my meter although it's the new type outside the house and quite visible, so they sent an estimated bill for months and months, this was right through the bad Winter we had.

Then during the Summer, when we are not around as often and obviously don't use as much power, they took out 1700 Euros in 3 separate payments from my bank account.

After several visits to their office in Mora d'Ebre, and arguments in Spanish (insults under my breath in English) I decided to go to the equivalent of the ombudsman, which is usually based at the Consell Comarcal in the bigger towns and cities, ours is Mora d'Ebre.

I wrote everything down in Spanish, showed evidence of the bills, the discrepancies of more power used during Summer than Winter etc etc etc.

They took my case on, and within a few weeks, I had several letters of apology, and they refunded me almost 700 Euros...........that's some huge mistake/misread meter/cockup/fiddle or whatever you want to call it.

Find somebody who can help you with the language Northlea and you should be able to find your Endesa account number at the top of any bill.

Also say you are going to change to another provider, that's always a good one, freedom of choice and competition arrives in Spain at last.

My 83 year old Dad always says they are between 25 and 50 years behind over here. Sometimes a good thing, other times not.

Hope this helps.