Consultant

I'm a sub doing asbestos remediation.  $300K contract, a set number of feet of pipe.  1/3rd through the work, get stop work and T for C.  Have several (unsubmitted) pending REAs in work for changed conditions (pipes not turned cold when scheduled, etc) worth about 100K.  Prime requested we sign releases for amount already paid.  We declined and submitted settlement proposal 5 months ago, for paid costs plus $100K for costs incurred plus a reasonable fee %.  Since, prime has ghosted us, ignores registered letters and hangs up on us.  CO won't reply.

Contract has disputes, but that requires execs to huddle and fail first.

Sent legal letter several months ago explaining primes role and obligations - ignored.

Question - on what basis should we sue them?  The Specific Performance of dealing with the settlement proposal on this terminated but unmodified contract?  For entry into the dispute process?  

Other suggestions?

Thanks in advance.