NightHawk AC1900 WiFi Model C7000

I replaced Xfinity's router with the one in the subject line to try to save some money. It was a grueling experience getting it hooked up due to Comcast's poor customer service. I finally got it set up but when we tried to use our Kindles it kept wanting to sign into the router on Kindle. Not a doable act. The font was miniscule and wanted security questions answered and so on. Just not doable. I talked to Amazon. They said the router probably had a "captive wifi" similar to the ones in hotels where the guests sign in. They told me to contact Netgear and have them turn it off. The Netgear experience was two hours long all for it to end with a request that I return the modem. She first said no there is no "captive wifi", then later, over an hour later, she said she was trying to get it so it could be turned off. She gave up and told me to return it. I am hoping there is someone out there who knows what to do. I had such a hard time getting it set up with Xfinity I really don't want to return it if it is possibly a simple fix. Does anyone know how to get the Kindles to simply pick up the wifi like it has been for years already? Thank you so much in advance!

Little Lisa