Hi Jaair,
As far as I know, Spanish is still on the list of ICAO official languages (English, Spanish, Chinese, Russian, Arabic, French) so it can be used, although all pilots and controllers should possess at least level 4 English if they will be operating in an international environment. In my current Middle Eastern country, the authorities are doing a very good job of trying to lift our English standards and actively discourage the use of anything other than English. Keep persisting with English; it should be the safer option and will help our Spanish colleagues lift their standards, which aren't lauded by folks who use the services there.