After finishing about 10-15 surveys I noticed that the emails stopped coming. I contacted the support and got vague response:
"A search of our records indicates that you are not an active member of American Consumer Opinion®. There could be a few reasons for this. Your account may have been flagged for non-compliant activity, or you are signed up under another email address (besides this one). If your information was flagged, this could be due to several reasons.
Your survey or registration data was not valid.
We have found that you were not being compliant with the American Consumer Opinion® panel's Terms and Conditions agreement."
They never responded to my demands to clarify and give my a specific reason for deactivating my account.
Of course it happened as soon I've earned my first 100$ worth of points.