Several months ago I forgot what product's survey I experienced the exact same thing. Then another one asked if you were willing to do another survey you earned additional points. NOTHING, incl the initially successfully finished survey. Did not bother to send an email but since then anything about whether you are willing to do an additional survey to earn additional points, I passed.

Then I was booted on a survey from JD Power at 67% completed, saying I was not qualified. This time I sent email to complain. They ended up gave 50% of the credit because they found "I spent more than half of the time on the survey which should have stopped accepting new participants at the time but somehow let me thru..."

My goal doing the surveys are for the ability to extend airline / hotel programs so I only do a bunch once every 7 to 10 days. Most of them were 0.25 per pop but once I got about $10 for that exercise I stopped wasting my time.