Arris S33 connection speeds

I was having issues with my internet service over a month ago. And, of course, I received the same message [Edited: remember what grandma would say] that there is no issue with my internet service. 

I was unsure if it was the Xfinity modem, so I purchased an Arris S33 and completed the self install through the app. It showed up in the app as an Arris S33 and being supported.

Two days later, my modem was disconnected from Xfinity service. First chat [Edited: remember what grandma would say] through the app told me they fixed the issue and it would take 2 hours to take effect.

I waited the two hours, and it affected my work form home position as I had to leave early because of lack of service.

I had contacted [Edited: remember what grandma would say] through the app again to someone that was able to fix the issue and I was able to reconnect to Xfinity service.

I assumed that because the Arris S33 has advertised on the box that it would work with the higher speeds, since I am already paying for 2100 Mbps speeds, which is available in my area, but not in all parts of where I live, where they are limited to 1200 Mbps speeds.

I see my modem connected at DOCSIS 3.1 speeds, so is that for 2100 Mbps speed only, or for also the 1200 Mbps speeds.

I am worried about going over my limit, so I paid the fee so that I am not capped and charged extra.

I see only a $3 difference from 2100 Mbps and the 1200 Mbps speeds.

By the way, Xfinity did come out and replace the line, because the tech saw my signal all over the place. The installation tech spliced the line outside of the box and water got into the connection and sent my signal all over the place.