Since speed increase Arris TG862G no longer works :(

The good is that the xfinity speed in my area increased.  I have blast so the download speed should have increased from 250 to 275 mbs.  Not sure if the upload speed increased.

The bad news is my internet stopped work.  The tech told me that my telephony modem is no longer capatible and rented me a comcast modem at $13 a month.  He suggested that if I wanted to buy a modem to get an arris or netgear with docsis 3.1.

My telephony modem that no longer works is a arris tg862g and is DOCSIS 3.0 with 8 channels down and 4 up.  I look at the suggested telephone modem arris TG1682G which is suggested through the xfinity approved 3rd party equipment and it is also DOCSIS 3.0 but with 24 down and 8 up.  

To complicate things when I check the xfinity approved equipment just by zip code, speed of 250 mps, and 400 mps I get a different list then when I actually log in.  I get more if I just put by zip code.

The telephony modem from  xfinity is tg1682g which is DOCSIS 3.0 with 24 x 8.

I want to buy a budget telephony modem from amazon instead of renting.  Can I get any xfinity compatable telephone modem (from their web site) that >= 275 mps with docsis 3.0 and 24 x 8?

Also any reason why my old tg862g telephony modem stopped working afer the upgrade.

Thanks in advance for your advice