My take? I think they're playing games. Especially suspicious am I, since they've already cut you a check. Much as I am really loathe to suggest this, it may be time to check with a lawyer _with experience_ on this. A consult should cost nothing. And even if you do have to pony up and hire a mouthpiece, he'll make sure it's worth it.
My 2c, and check with your mentors...
'73 R60/5 Toaster