My docsis 3.0 router supports 340mbps, rented routers are a scam.

I placed an upgrade order for the internet ultimate, I noticed it has been processing for about 8 days, so I talked to a chat rep who told me my router isn't compatible with my upgrade to the internet ultimate, she claimed that my modem router only supports up to 150mbps wireless due to it being docsis 3.0 and I'll have to rent a new one through Cox. I explained to her that my modem router actually supports up to 340mbps wireless and 1gbps wired, and that I mainly use the wired service, I even offered to link her the specifications listed by the manufacturer to prove this to her, she ignored this and told me they cannot do it. I asked for a supervisor, she asked me to wait then disconnected on me. I'm not paying for a modem router that will not benefit me in anyway when I know my modem router is more than enough.