Discrepancy between billing and plan for internet speed

My bill for September 01, 2024 to September 30, 2024 is for an internet speed of 300 MBPS. I did not request an increase, and my plan still shows an internet speed of 150 MBPS and that is what I see when I run a speed test. The billing amount did not increase so I'm wondering if I should have received a doubling of internet speed at no additional cost. There is a message on the xfinity app titled 'Faster speeds are here' that seems to say my speed has been doubled. For a time in August, my plan actually showed an internet speed of 300 MBPS, but it later changed back to 150 MBPS. Any clarification would be appreciated.