Tashabella
You can certainly tell the DWP that you only want them to communicate in writing, it's unlikely that a DM will try and contact you but I have to tell you that some, not all, members have found it to their advantage to take a call as it allows them to explain their problems in more depth and to answer the DMs questions, so I would think carefully before ruling it out.
Gordon
Nothing on this board constitutes legal advice - always consult a professional about specific problems