Not sure whether you can change to another medical centre - you can change Drs ( I had to give the reason & language difficulty doesn't count... This should help.
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Making a complaint about doctors in Spain
If you are not happy with the treatment you have received from a doctor or health service, you have a number of options:
Fill out an Hoja de Quejas y Reclamaciones – complaints and claims form – at your medical center.Write a letter to the Servicio de Atención a Pacientes y Usuarios – the complaints department – of the relevant hospital/clinicSubmit a complaint to the local authority (Junta). In this case, you must send a copy of the complaint to the health center and one to a ‘registro general‘ in your town. Ask your town hall (el ayuntamiento) for details.
)Cheers
Elinspain