XB8 is giving 0% out of my 1GB plan

recently I experienced that my internet speed drops to significantly low - almost 0 percentage out of my 1 GB plan.  I called xfinity support, the diagnose test couldn't find anything, the gateway is online, but download speed is very very low, around 2mb out of 1 GB plan. The box was hot, and I can not even remote restart the box via Xfinity app, It asked me to restart manually.  The technician asked me to go to store and get it replaced, and I did. At first 2 days, it was fine, I'm getting 1 GB download speed, but on the 3rd day night, I'm getting 0% out of my 1 GB plan again.  I unpluged power for 30min, and plug it back again, and I'm still getting very slow internet. Why it is happening like that? Does it mean the XB8 I received from Xfinity store is a defect one again? Is there any better Xfinity gateway I can use different Xfinity gateway better that XB8?