Bundle package frustration with internet

I ran a speed test and got 300Mbps.

the modem included in the package DOES NOT support 300Mbps. 

Both cannot be true.

What you're really asking Cox to do is divine from your online bundle building that you have a 3 story home and would like to have the full 300Mbps available through Wi-Fi in every square inch of that 3 stories from just a single modem/gateway regardless of the Wi-Fi capabilities of the adapters in the devices you're connecting with.

That's just an unrealistic expectation.

I suspect in the fine print there was the standard dodge, "The 300Mbps is based on you having the very best equipment money can buy and even if you do cannot be guaranteed by Cox anyway. No way, no how."

I also suspect the bundle you built specified a modem was included and you asked to insert a customer owned modem into the bundle and that was the option that was not an option. Nothing to do with the modem not being able to be provisioned.

You have, I think, a 30 day, "I changed my mind"  window. Use it. Don't build a bundle online. You'll get pigeon holed into something that's not quite what you want. Call them, or better yet, if possible, go in person to one of their storefronts and tell them what exactly what you need and expect. You'll still get a bundle discount. Probably better than their online offering.