It sounds like Congressional offices are dealing with a backlog of their own related to immigration processing delays.
In my opinion, this just makes the mandamus lawsuit option that much more important. According to Roll Call article entitled “Immigration Agency Backlog Weighs on Congressional Offices”:
“Member offices have fielded a growing pile of requests for help to speed their cases through U.S. Citizenship and Immigration Services, the backlogged agency that handles requests for visas and other benefits.