I have been a very happy customer of Arrakis (http://www.arrakis.com) for the past seven years. The company is based in Seville and is part of BT. Many of the staff speak English – that is say, that when I speak to them in my accented Spanish they usually try to answer in English.
They are not the cheapest supplier but I have had not a single problem in the last two or three years.
However, when I recommended Arrakis to my neighbour last year they made an complete mess of everything. So they are not infallible.
On a separate note, I recommend buying the modem and router from your chosen broadband supplier rather than the computer shop down the road. If you have a problem and the equipment used is not supplied by the broadband supplier you may find that telephone technical support is very limited.