Re: "despite me being very reasonable"
Trying to short circuit by going to sales is just entitled "I'm too important to get in the queue with everyone else!!"
Or put differently: hampering the sales dept will make it more difficult for the company to add more customers, thus helping to limit the problem of an overwhelmed support dpt.
All within reason of course. There's a difference between having to wait five minutes midday and being put on hold for half an hour (or more...) no matter when you try calling. "Your call is important to us, you just have to wait for an hour while we answer other calls that are also important to us"