I've had a few questions that I've asked Steam Support and never got a response for. I think that might count as the worst considering they didn't even bother to try.
I've also had multiple times where someone didn't even understand their own product. I was one time trying to fix a computer and was trying to ask the company that built it about the problem. They didn't even know which wires went where in the computer and basically left me with a 50/50 chance of fixing the problem or creating an even worse one.
There was also the time that I contacted a company to ask a question only to be sent to a different department only for them to send my call to a third department only for that third department to send my call to the one that I originally contact. It actually is sort of funny now that I look back on it.
But probably one of the most damaging to me was at my former college's bookstore. They were supposed to send an e-mail to alert me that I had received the books that I had ordered. As a result, I decided to pick the books up the day before classes and wait until mine got in and just return them. Conveniently, it took them until the day after I could get my refund to e-mail me (did I mention that my order started getting process the first day anyone's in the college possibly could?). Oh, but it gets better! When I made my disappointment clear, they acted like they were giving me a refund (i.e. gave me some cash) and sent me to the office to finalize the transaction. I instantly knew that there was a problem, though, when the office said that they weren't actually able to do anything and that they had no idea why the bookstore kept sending people like me over to them (yes, I wasn't the only one facing this problem). I later found out that, despite giving me some cash to shut me up, the bookstore ended up charging my financial aid the amount that they gave me in cash. The end result was that I still ended up paying them for the books! And you want to know what the college did about this problem that, as I already said, was something multiple students dealt with and the office clearly knew about? Nothing!