As far as I know, a boletin
is needed (at least officially) to change the name on the contract - although whether or not this is enforced seems to vary from one area to another. 150 euros is about right for the boletin. I'm not sure about having a right to
expect it when you bought, but you certainly would have had a right to request it, and use it as a negotiating point, if none existed.
The work carried out outside your house, I can only assume must have been to replace the cabling from the meter to your fuse box. Anything else is surely not your responsibility? Copper cable is expensive - but even so, 600 euros? How far away is your meter?!
I would accept the charge for the boletin, since you didn't request it from the seller (next time!) but I would certainly query the rewiring cost and ask for some justification of what this amount is for. And since you never authorised any work, as you say, why are they now billing you anyway?