HELP: I cannot get support from Dell

I bought a used Dell M6800 top-of-the-line laptop thru Amazon in late December 2015 and find that the Dell Service Tag number was not registered. Therefore, after many long phone calls to Dell, I'm told I cannot buy an extended warranty and I cannot even buy case-by-case support. I'm treated like a criminal because Dell people think this laptop was stolen from Dell and perhaps it was. But I bought it legitimately and can prove it. The Amazon dealer, located in Chino Hills, CA (ASN Computers) says he bought it legitimately also. During my many phone calls to Dell, I'm told your inventory system shows that this laptop is located at Dell and was never sold. Is there anything I can do to fix this. The dealer will not take it back, Amazon denied my claim, though I'm appealing, and I'm virtually out of options. As an innocent buyer, won't Dell help me to rectify this issue so I can get help thru Dell? My immediate problem is that my fingerprint reader does not work in Windows 10. It works to register my fingerprints and was working after a hard restart, but now, after the latest Dell DDP update a few days ago, it doesn't work at all. I'm fairly sure I need to uninstall Dell DDP and then reinstall the latest version, but there is no apparent way to uninstall this app, at least not without help from Dell. In the long run, I'm more worried about more serious problems for which Dell will not help me. Thank you.