"Good luck getting written response from" That sadly seems to be the way business in general is done in the US these days. Insurance
labs, all sorts of places that are under legal
obligations to deal with their correspondence in a rather formal manner, simply throw some of it out and say "We never got it." And that's actually a profitable way for them to do business, because folks with complaints get tired and just drop it. Or, if nothing else, the payments (etc) go out next month when the bill is resent, instead of this month.
(Of course, no one would ever just throw out the incoming mail or faxes. It really gets adbucted by those four foot tall gray aliens with big black eyes, you know, "Alien Abuction" ? )
Sometimes they play "We never got it" despite the letter being sent certified and return receipted, and if you ever want to hear a clerk backpedal hard and fast, that's when you remind them that if their mail really is disappearing internally, you can help solve that problem by calling the postal inspectors. And their manager. "Oh, wait a minute, here it is." Ahuh.
, a first class stamp and a reasonable wait (two to four weeks, no more) is good enough to get a reply. Followed up with the fancy stuff if it doesn't come.