Gertrude
They need to contact ATOS to find out what is going on, if this is a re-assessment and they continue to fail to attend the interviews then there will come a point, even for someone with mental health issues, when ATOS will return their file to the DWP as a "no show", which could easily result in their claim being closed.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems