Have you rebooted and/or pressed the reset button on the router? Can the PC support the gig?

Verizon uses network terminals to provide the signal of all services. Not really sure how it works with your provider, but maybe you have something similar tp Verizon's and it isn't compatible with that speed?

EDIT: Just read where you mention you allegedly are receiving what you're paying for. At AT&T they're going to tell you it's either the Ethernet cable or the PC. You could try with another router, though. 

Last edited by Metallox - on 24 September 2019