Hi, Eskandar, thanks for answering again.
Trying it again with Dehkhoda was an option, but then I thought about it and definitely not. If they took almost 6 months to give an answer (and two weeks after my course started)...
I didn't mentioned before, but I spent nearly 200 € in paperwork: a few legalizations, an official translation... I have made language courses in Ireland and Russia and I asked some friends of mine who also made this kind of language courses, and it never takes so long to recieve an answer after all the paperwork and stuff, at most one month. So there is no way with Dehkhoda. Besides, I sent them an e-mail asking for explanations and they never replied me -and I was very polite-.
I asked to the Iranian Embassy in Spain, but they are not very helpful -as you say-, in fact they only told me about Dehkhoda telling me is the best place to study Persian in Iran, bla bla bla. But I can't believe there is no way I can't find another place (not Dehkhoda) to study Persian in Iran for a few months -3 or 6 minimum-.
I'm pretty sure there are academies for foreigners but I was hoping to find some special academy/institute for foreigners like Dehkhoda with student accommodation and with a visa student, because that's another "problem", I don't know how much time I can stay in Iran with a turist visa or a student visa.
I have seen that the University of Esfahan offers Persian courses (for one or three months), but are very expensive -2,000 $ for three months- compared with Dehkhoda. I also like Shiraz, but I had already made me illusions with Tehran or Esfahan.
I'll keep trying it. Anyway thanks for your recommendations.