Spanish spouse schengen visa only marriage certificate

Hi This is my inquire,

My wife Spanish national gave birth a month ago and she is going to spend the maternity in Spain, I will be travelling the weekends there, but I have got a residence permit in the UK as 6 years has passed so I am not longer using the EEA card. In order to avoid fighting at immigration airports in Spain, I have applied for a schengen visa, I went to VFs global and I paid a fee that I shouldn't do it , knowing now that under european law , i have got the right to go to the embassy and apply directly for free. And they told me that I need a letter of invitation from her parents I only showed Libro de familia, marriage certificate and my plane tickets.

So I just want to know that in the case they ask for a letter of invitation, I can say that it is not necessary under european law, and how i can complain if this goes further.

Thanks for your help

If you run into trouble contact Solvit (bottom of this page:
http://europa.eu/youreurope/citizens/tr ... dex_en.htm

And more info can be found in the stickies here and also on the Handbooks on EU Home Affairs:
http://ec.europa.eu/dgs/home-affairs/wh ... dex_en.htm