Firmware Frustration on CM400

About a month ago, the Netgear modem I have been using with my ISP for 2 years abruptly stopped working. After multiple tech visits out to my place, and replacing the modem with the same model to no avail, my ISP finally determined the problem to come from a recent series of upgrades to their network they did recently. They told me the firmware might be out of date on my modem--they said it should be 1.01.17 and because I did a few factory resets to make sure the modem was running properly, my firmware was downgraded to 1.01.10. If this is correct, I cannot connect to my ISP to update the firmware. Is there any possible way to update my modem?

Also, if this helps, the issue with my modem has been that downstream will bond OK, but upstream will not.