How to submit a death certificate in order to be able to make ANY changes to account

As stated... fairly basic thing, seems nearly impossible to accomplish. Grandfather passed away in 2014, and have been unable to make any changes to the account since (my grandmother). Since then she's inquired, but being that she cannot travel, has no computer or internet (though that seems not to matter either), and with it not being possible over the phone... it seems purposefully difficult by design. Especially given the search results on the xfinity site, with some ENDLESS results of folks asking this same question, and then having an xfinity rep tell them to DM them (no link or explanation as per HOW to do this), which isn't even a proper option on the site at all. This seemingly being the nearest equivalent to a "DM" option here, another post asking for help to end up in the search results to infinity, asking the same thing. No official means, no web portal or option to simply work through using a digital upload, no over the phone options... just purposefully hard to do, even in the worst possible scenario, the loss of a loved one... who happened to be the account holder. So xfinity sees dollar signs via complications... figures. Classic comcast. . .