Upgrading gateway

I was eligible for a gateway upgrade (said the gateway I had couldn't handle the new speeds in my area) and I was having issues with my current XB6 gateway (dropping wifi multiple times per day, used to only drop once or twice a day). I went to the store since it was closest and fastest and told them I was eligible for an upgrade (after trying to troubleshoot on the xfinity app and waiting over an hour for someone to call when the "assistant" couldn't help me). The employee replaced my XB6 with another XB6. I am still having the issues with the wifi dropping with the new XB6. My plan states I have upload speeds of 1200mbps which according to xfinity website the XB6 can only accommodate speeds of 1000mbps. I figured the upgrade would be the XB7 or XB8. Is there a way to get upgraded to the XB8 to replace the XB6 without upping my bill? I have tried calling but keep getting disconnected. Thank you!