Ok, well a couple of thoughts here. First it's never a good idea to make large financial decisions from an emotional place. So my advice is also to give this some time and additional thought. If you then decide that you still wish to sell off your equipment at least you'll be assured that the decision was more of a rationally based notion rather than a spur of the moment knee jerk reaction.
Second thought, the customer service you get nowadays can vary widely based on something as simple as who answers the phone on the other end. I'd agree that you got some bad customer service here - sadly though I don't think you'll find a huge difference in switching to Canon, or Sony, or anyone else for that matter.
A couple of thoughts on dealing with CS reps. Step one, never call up and immediately demand to speak to a supervisor, when you do your shooting yourself in the foot. Sure, it seems like a good idea to impress on them how angry/upset you are, etc.. but thing you have to understand is that the CS supervisors, for the most part, are less knowledgeable about the actual internal day to day workings of the system. Most supervisors are there to "supervise", more or less just to manage the people under them.
Many are often hired from outside the company and know far less about the actual day to day how to get stuff done aspect than the person who answered the phone. You'll almost always get better results if you don't have to escalate a call to them. There are some exceptions - but your best bet is to work with the CS rep first, and only go to a supervisor if it's absolutely necessary.
Step two, when the customer service rep tells you there name, repeat it back to them just as if you were writing it down. I recommend you write it down, but even if you don't make a show of the fact that you are. They'll launch into their spiel, when they do ask them for their last name, last initial or id number. Repeat that back to them as well, impress on them that you are making a record of who your speaking with. You'd be stunned at how much better customer service you'll get if the person on the other end of the phone thinks that this might eventually come back to them. Lol
Step three, let the rep know you are upset but qualify that by letting them know that you are not upset with them personally. When you make it personal you remove any incentive the rep might have to go out of their way to help you. If you let them know that you are upset about the situation, but not mad at them personally and don't get nasty with them, it really does make a huge difference in how far they will go your behalf. It's about getting the rep on your side. Not always possible, but believe me when you can this makes a huge, huge difference.
Just a couple of general tips for anyone that might need to deal with CS over the phone in the future.