Sorry to hear your situation. First of all Comcast has the WORST modems on the market. I have been with Comcast for over 10 years and had nothing but trouble with their network hardware. SOOOO i decided to purchase my own and stop renting their junk. never had a problem since. Here is what i have purchased. I'm sure there maybe some newer models out there but take a look.
Comcast Compatible and better then the one Comcast leases: Arris Touchstone TM822G DOCSIS 3.0 8x4 Ultra-High Speed Telephony Modem
Beat Buy: RT-AC66U Dual Band 3x3 802.11AC Gigabit Router