Can't get my iPhone 5 back to factory settings

All instructions I am seeing do not work in my case.

I recently bought a 6 to replace my 5 and am having some
issues resetting my 5 to factory settings. For some reason my 5 thinks my
icloud password is invalid when I go to iCloud and select my name and e-mail at the top (it is not incorrect – I can
log in on icloud.com and my 6 just fine.) I am on iOS 8.1. I would love to “erase
all content and settings” but when I enter my password in I get an
error “Verification Failed: There was an error connecting to icloud.” When I go
under iCloud I get the same message. I also get the same message if I try to
turn off the find my phone function. If I got to icloud.com it recognizes both
of my phones. Also, I have tried all of this connected to wi-fi and not connected. I am able to do every other reset on the reset page -

just not the one I need...Not sure what to do to clear out this phone. I would like to sell
it. Thanks!