motorola mb7621 - extremely slow speeds

I have been using this Motorola MB7621 for about 6 months and everything has been going great but just about two weeks ago I started experiencing extremely slow speeds (around 5-10mbps download). My Xfinity plan is 800mpbs. This is making it almost impossible to work from home, which I do full time. My zoom meetings cut in and out constantly which is the main problem. I reached out to Xfinity and they of course blame the modem since they don't own it. Can anyone help here? I logged into the modem and checked the connection and everything appears fine, but I'm not a hardware / network guy so I'm at a loss and really hoping I don't have to buy a new modem or start paying xfinity the rental fee. Help!