Complaint sub-issue: Credit card company isn't resolving a dispute about a purchase on your statement

I'm afraid that I can't provide exact dates ; this has been going for 13 months. I'll try to make this as clear but as brief as possible. 

I ordered a guitar for {$5100.00} from a merchant in XXXX in XX/XX/XXXX. He didn't mail it in the specified amount of time so I cancelled the order. At that point, the merchant said that he'd already put the guitar in the mail but he could stop it, even though he'd still have to pay shipping. I stupidly agreed to split that {$160.00} cost with him, a choice that has added to the problem. 

As weeks went by, it became clear that, even though the merchant said he'd refunded my money, he had not. I tried to work with the website I bought the guitar over, one that said it guarantees all purchases but they said that because the payment went through XXXX --  irrespective of whether we used XXXX on their site -- they couldn't guarantee it. So I went to XXXX and tried working with them, but that became impossible. That website is called XXXX, and as far as I'm concerned, they're as much responsible for this as Discover. They charge large fees that are meant to provide protection against scammers like this. 

So in early XX/XX/XXXX, I filed a dispute with Discover. In XX/XX/XXXX, Discover mailed me to say that they found against me, even though they had documents that I'd submitted in which the merchant said he owed me {$5000.00}. When I called, they agreed to reopen the dispute. A few months later, Discover claimed that they found in my favor. That meant to them that they refunded {$80.00} of the original {$5100.00} to my card. Clearly, they made a mistake and refunded {$80.00} instead of the {$5000.00}.

From here, the black hole that is Discover began. It took months for me to get Discover to  admit that agree that {$80.00} was the shipping charge, not {$5000.00}, as if anyone would pay over XXXX XXXX to ship and item worth less than {$100.00}. I was then told that I needed to submit more documents, which I did. Since then, it's been one excuse after another : They required me to get documents from the merchant, even though it's not obvious that he's a scammer ; hence, why would he give me documents that prove that? They have brushed me off each time I call, saying that the case has been escalated and someone will get back to me shortly. 

Of course, no one ever does call me back. Not once. I've had at least 15 supervisors promise me they'd call back. And every time I call, I have to go through their whole system before I get a supervisor. That person then needs to review over a year of notes, so they put me on hold for half an hour. They then tell me that they'll make some notes and have someone call me back. If I'm lucky, they'll tell me what the last action taken was. For the last four months, that action has been something like this : " Last week, the group that decides these cases met and went over your documents. They were unable to make a final determination, so they've escalated the case. '' It has probably been escalated from one final group to the next " final '' group half a dozen times. 

Meanwhile, the charges remain on my card, the interest accrues, my credit is negatively affected, and there is zero leverage that I have over Discover, absolutely nothing I can do about this situation except to call ad infinitum. To be fair, I've done that part for over half a year and it's made no difference. After all of this, I'm right where I started : facing the charge on my card, in possession of no guitar, and being told nothing more specific than that it's being worked on by the new escalation team. 

From here, I have no idea how to proceed. So I'm turning to you for help. Hopefully, this write-up is coherent without being too detailed. I've left so much of the pain and heartache out of this because it isn't absolutely required for the matter at hand. Please let me know what more information I can provide, though.

A final and important note : Only one supervisor gave me his complete name. That is XXXX XXXX, a supervisor who works in the XXXX, OH, dispute office. He also admitted that Discover made an error, that he would make sure it got fixed, and he made clear that while it was too late to recover the funds from the merchant, Discover would pay it because it was their mistake that made the timeline pass for when they could have recovered the funds from the merchant.