I expect that the percentage of politicians and public services/institutions who have even heard of xcancel is incredibly small.
The real way to combat this is to write to your representative. The best way is probably to ask questions about something you care about, and when they reply "I've posted about this on X", tell them you are unable/unwilling to use that platform, and as a government official they should not be using a closed service as the sole means of communicating with constituents.
Of course, that probably still won't work, since politicians are lazy, and most care more about fundraising and getting re-elected than doing their jobs, but it's probably the best you can do.
The real way to combat this is to write to your representative. The best way is probably to ask questions about something you care about, and when they reply "I've posted about this on X", tell them you are unable/unwilling to use that platform, and as a government official they should not be using a closed service as the sole means of communicating with constituents.
Of course, that probably still won't work, since politicians are lazy, and most care more about fundraising and getting re-elected than doing their jobs, but it's probably the best you can do.