slow internet speeds but speed test shows something completely different

Hello santi_365 and thank you! I really appreciate you being a member of the Comcast Family! When you performed the speed test was this a hardwired connection or through WiFi? May I ask what device you used and its max download capability? 

For a test, what do you get with that computer being hardwired directly to the router / gateway device with an ethernet cable ?

That's too bad because it's a valuable test...... See if anything here applies;

https://forums.xfinity.com/conversations/your-home-network/connection-troubleshooting-tips/602da777c5375f08cdea3db9

Good luck !