I got my Note 7 on craigslist. T-Mobile won't exchange it. Trying to go through Samsung but they don't have the process in place for third party exchanges. Been raising hell trying to get an exchanged unit especially since I get annoying recall pop ups and I have a first ever on a phone of mine: a scratch (thanks gg5).
Anyways it sucks not having fast charging. It's a huge feature for me. Samsung is sneaky too saying it's fast charging when it's not.
That really sucks. Sorry you're going through that. I have to believe that especially with the government mandating the recall, Samsung will have to replace your device for you. I wonder if it would be worth your trying to contact the US Consumer Product Safety Commission directly about it? They've mandated Samsung to replace all of these devices, and I don't think Samsung wants to get on their bad side just because you got your phone from Craigslist.
Another idea if you're not opposed to trying, is to use Twitter, and tweet about it politely calling out @SamsungMobileUS. They know that Twitter is public, and most companies respond to tweets a lot more quickly than any support call. Typically they have a separate group who has more authority than support and monitors their Twitter feed.
This has backfired on people in rare cases where they've tweeted something that was false, and very damaging to the company in question (one or two airlines have sued), but if it's accurate, there is nothing they can do. I've used Twitter for this about 3 times in the last 2 years when a company left me no option. In each case, the issue was resolved within an hour of my initial tweet. In each case I then tweeted again to thank them for resolving it so quickly.