So I reserved one of the offers in Erasmusu.com for a hostel in Madrid for the whole month of September, then when I got there, they got my credit card and charged me yet again, and I can't get in contact with anybody from their team to confirm a receipt so I can get a refund from the hostel.
Conclusion, it's not recommended at all to reserve anything on this website, zero feedback and I lost 350 euros.