Could be translation and maybe they meant the box that houses the meter needs to be replaced or they could be referring to your consumer unit (fuse box)?
I replaced my exterior box because I want to install dual meters and I had to bring the box/housing up to the new standard. It's a double door grey box with a electricity hazard sign on it etc.
But they always fit the final meter(s) etc
The problem with being disconnected is sometimes they make you bring your installation up to current (always changing!) standards and require a boletin which I think is some kind or report/certificate from a registered electrician.
I would suggest you speak to a Spanish electrician who can talk to Endesa and find out exactly what they meant.
It's a bit of a pain to change the box/housing be cause the new type box is much bigger which means chiselling out and then re-fitting!!!!!