I see the irony of Dan's response - nicely point out they are being jerks and congratulate them on finally communicating after a year's time.  If we're talking big bucks though, I'm not getting out the sarcasm arsenal, I'm employing the legal.

People who won't accept accountability lash out.  Whether they're non-paying clients or independents/vendor managers/others who have 10 excuses why an order isn't back 2 days after promised or better yet, just go MIA until you threaten to cancel it, all come down to the same.  Posturing, defensiveness. 

Just pay your damn bills, stay in communication with everyone and do as you say you'll do.  Hmm, sounds so simple doesn't it yet I've never heard of any other business with so many on both sides not doing any of the above!