I know this is old thread, but man do they mess with you. I just did 3 surveys, with one saying I got 175, and two others say I got 5 each credits, and I have yet to receive them. So I think they only want what they want. I think they also have someone monitoring the surveys and just take their sweet time rewarding credits.
It makes it nice to keep your wallet from being used, but come on. If you want to make it easier for us to get credits then make it easier by rewarding what you say we should get.