Gigablast requires Panoramic Wifi Modem? That's what she said.

I contacted many cox agents and most of them told they cannot activate my own modem because my account is special. I need to use a rentan modem or call to another yech support. I tried again and again, and eventually one agent successfully activate my modem. I think there’s a big difference in knowledge among agents. I guess all other guys just tried to replace the modem in the account but the last guy stop/reinitiate the service with new modem.

omahaomaha

That's total BS and a marketing ploy to get you to spend more money.  I have my own cable modem and router and I've never heard of a special account.  Now I have heard of a roommate account, where you can have more that 1 service in a residence.  Perhaps that's what they were referring to.  But you can use any approved modem for your service tier based on Cox's own website.  I have gigablast service myself.  I know of a firmware certifier for Cox and he's quite knowledgeable.  He tests cable modems mostly but some combination modem/routers too.  Don't be fooled by some knucklehead in customer support that doesn't know what they are talking about.  Request to speak to a level-2 supervisor immediately, and tell the initial rep that they can't help you at all.  You've been through this before.  All the initial support contact does is try to upsell you and get you to use their equipment for a monthly rental fee.  It's more money for them.  Hell, you should know just how expensive it is just to have internet service.  More and more people are going to internet only, so Cox will jack up the price on that standalone service to maximize profits.  It's all about $$$ with a large corporation.  Let's see if someone from customer service or an admin on the forums reads this and puts you in contact with the appropriate level of tech support, without charging extra money.

The rep lied to you.  These reps are charged to nickle-and-dime you through rental fees and superfluous services to increase revenue.  You'll need to keep fighting the runaround try escalating to a supervisor.

I have my own ariris sb-8200 with gigablast. I finally went to the COX store and discussed. The online and phone operators/salespeoples were less than honest almost 100% of the time. 

Contact tech support not customer service. Customer service agents are idiots. Let tech support know you purchased your own DOCS3.1 modem and want it setup to replace the Panorama. But if you have digital telephone with Cox they probably will require you to have the Panorama because you need it for the phone line. Check to make sure they aren't charging you for telephone service.