A reasonable approach? When I'm in doubt, I just go with the truth. They could have said "Hey, we hear you, we're starting a group to figure out how best to resolve your issues." or "Hey, we've already been working on this, we'll get back to you in a couple of months." Or even a "Hey, we get you aren't completely happy, but we just don't have the time to address your concerns right no, but when we can, we will."

Any of those would have been better than perfect silence followed with, we'll see what we can do.