I have had to chase payment from this MSC more than all others combined - and I have done more work for about 30 MSC's than I have for Cirrus. When I take their work, I always do so with the recognition that chasing payment is part of the game. I am not at all surprised that they are even less reliable right now.
That said, I have always, eventually, been paid. If they requested "a little more time," give them about two weeks (It's been four months, so they really shouldn't need "a little more time," but whatever. Then contact the owner: Monnie Howard (mhoward@cirrusmktg.com). I have always had good results when contacting her directly.
Hard work builds character and homework is good for your soul.