That's true, but there is a 'hack' to get around that. Generally new questions arriving at the office will not have prepared responses. New text can not usually be written by the staffers without being reviewed.
So, the trick is to raise 2 (unrelated or related) issues in your letter. Issue one is the real issue you are concerned about, and the other needs to be something low profile that will not already have a canned response.
That way a reply will need to be drafted by staffers and reviewed by someone (hopefully the actual politician).
I've tried that also, without really having any success. Perhaps it relates to their profile and volume of correspondence? Most of my (mostly negative) correspondence over the years has gone to my now-former Congressman (and former House Majority Leader) Tom DeLay, who I can imagine was pretty busy.
So, the trick is to raise 2 (unrelated or related) issues in your letter. Issue one is the real issue you are concerned about, and the other needs to be something low profile that will not already have a canned response.
That way a reply will need to be drafted by staffers and reviewed by someone (hopefully the actual politician).