Netgear CM3000 Nightmare

Last week my network went from 1.2 gig down to 0.1 meg. After trying everything, I reluctantly called Comcast support. First thing they said was "I can't see your modem from my end". This seemed ridiculous, since I was able to use the internet, albeit very slowly. I had an external Comcast IP address assigned, and I had QAM256 channels Locked. The interesting feature was that the single OFDM downstream channel that provides the DOCSIS 3.1 ability (my 1.2 gig) was "Not Locked". Power level for that channel is showing -21 dBmV, which seems out of range, but I have found no reference to power limits for the OFDM downstream channels. My upstream is unaffected in all this.

The next morning, my speed was somewhat restored, but with a limit of 1 gig, reflecting the "Not Locked" OFDM channel.

During the initial support call, the support person decided that my modem must not be provisioned correctly, even though it's been running fine for the 7 months since I purchased it. Upon looking at the modem after concluding my call, I discovered that my CM3000 firmware had changed from V5.01.02 to V6.01.04! Nothing had been said about this. I never received it, but this year Comcast had sent a V6.01.03 to some CM3000 owners with disastrous results. This V6 was pulled back and V5 was put back. Looking at the Netgear support site, they are still publishing the official Comcast version as V5.01.02.

A tech came out today and declared that my coax signal was peachy keen, so he declared that I had a defective modem. Given all the clues showing themselves, I am finding this hard to believe, and continue to suspect something on the Comcast side is the problem. I then performed a Factory Reset. I then used the Xfinity phone app to Activate the modem, which was accomplished, again, providing an IP address and again, providing only QAM channels, with the OFDM channel still not locked, power again at -21 dBmV. I called support again, and once again, they claimed to not see the modem!

My biggest issue is that Comcast appears to be saying that because it's an owned modem, it's not their problem. If so, then how do I get the original V5 firmware, that I did not have the chance to approve, reinstalled??????