How have you been contacting QBs about this? Although there are some employees here in the Community, I'd be surprised if they could actually resolve a money issue like this. One of them hopefully will send you a private message with a Name and a direct phone number of someone that should be able to resolve the issue though.
But if you've been in contact with them repeatedly for 18 months and nothing has happened, then it sounds like you're going to have to spend some money to get your money. I'd have an Attorney reach out to them.
And for do diligence, which I'm sure the Attorney will ask you, did they give you any reason why they're holding back on paying you? Are they claiming they didn't receive the money or because of some other issue? If there's an outstanding issue, be sure to have actual documented proof of why they really own you the money.
