MMT has been refuted by me and by others right here:
https://forum.freecapitalists.org/t/an-austrian-critique-of-mmt/17182
and here:
https://forum.freecapitalists.org/t/mmt-redux/17764
and here:
https://forum.freecapitalists.org/t/an-austrian-critique-of-mmt/17182/6
Also I blogged about it here:
http://smilingdavesblog.blogspot.com/2011/08/are-mmt-and-ae-compatible.html
One of the threads has a guest appearance by Walter Mosler himself, with a long back and forth between him and the forum members.
I confess I seem to use a different system of logic than Fool on the Hill.