mvinas: I went through the 12 surveys and offers, only one was free (second life) and offered 75 credits which I still have not recieved. All the others required a credit card registration for a "free trial" (we all know how that goes) or purchase of some kind from the advertiser.
On the "offers" page, simply choose "surveys". I haven't had to enter any CC information... just answer some questions and they send me credits. There is a long survey (about 45 minutes if you're multi-tasking as I usually am) for 450 credits.. and a short one (25-30 mins while doing other things) for 150.
Just finished a "short one" a few minutes ago and bought a couple of sleeves of balls.
....
(Having said all that, I now see that you fly the "Bandera de México"... I'm not sure if this makes a difference or not. )