Some catering services apply right of admission reserved, in which case the norms for admission of customers must be visible on the front door.  Under no circumstance can you be banned from entering a place for being a lesbian, gay man, transsexual or bisexual. In case of being discriminated against or physically attacked, you need to know that: 

All public places should have a complaints book. In case of abuse or bad service, you are entitled to request a complaints form, fill it in and keep a copy of it. 

In case you are denied a complaints form, you can issue the complaint at the relevant customer care service centre. It is best though to contact municipal, autonomous, national police or guardia civil, ask them to turn up and report the case on-site. 

You must try and get contact details from people who witnessed the events, and submit them when you report the case to the police. 

If you have been assaulted, you must get an injuries form before reporting anything.