At the last moment I've been changed as an airline.

The company through which you bought your airline ticket, regardless of whether you booked online or in person at a travel agency, is obliged to inform you in a timely and appropriate manner of the identity of the airline you will be flying with. If they fail to do so, you can complain to the airline.

If the airline is changed after the booking has been made, the company through which you have made the booking must immediately, irrespective of the reason for the change, take all appropriate measures to ensure that the passengers concerned are informed as soon as possible.

In all cases, passengers will be informed at the time of check-in, and if check-in is not required for the connecting flight, passengers will be informed at the time of boarding.

Passengers can check, at the following link, that the new airline is not included in the list of airlines not allowed to operate in the EU:

http://ec.europa.eu/transport/modes/air/safety/air-ban/index_es.htm