Try something like this:
Response AS 'RawResponse'
WHEN response = 'N/A' THEN 'N/A'
WHEN response < 10 AND response > 0 THEN 'N/A'
END AS Response
WHERE promotionid = @promotionid
You had two columns returning as "Response", so I updated the first to "RawResponse".
As well, I just redid the case a little differently, but I would expect that yours should work as is as well.