I use to do their work too, but cut them off. They worked out a payment plan with me and have been keeping their agreement and sending the agreed upon amount every month. 
Unfortunately they did not watch their own recievables and got screwed by NES for 20K and Express Financial for 30K.
I think if you email Dan he will work out a payment plan with you, I personally wouldn't deal with their accountant, she should have been watching their money for them. I worked my payment plan out with Dan and Brian, they own the company.
I suggest you persist and email them every day until they answer up, thats what I did in addition to leaving messages, and it worked.
I don't think they are bad guys and I think they have a conscience, they do want to pay every one. They are still in business and have no intention of closing their doors and "screwing everyone" like some of these other companies have done.