[shitloadofbooks]

A few tricks:

1.) If they agree to a date when they will pay you, call them that day and "remind" them and get verbal confirmation that they will pay on that day. Ask that a reference number/receipt be emailed to you as soon as they payment has gone through. Call back later (or the next day if they don't pickup) to confirm that they kept to their agreement.

2.) Call them up and have a chat about the upcoming work and let them know that it's in danger of not being completed because you can't start it without payment for the past work. Stay professional and tell them from a strictly business point of view, you cant afford to lose any more money on their job. You'd LOVE to help them, but you just can't and you'll have to find work elsewhere and most likely won't be availible.

3.) If they screen your calls and hide behind receptionists or sub-ordinates, let the sub-ordinates know why you are calling. "Can you pass on a message for me? I am calling regarding invoice #780 for $7,400 which is now 55 days overdue." This always felt unprofessional for me, but it got results. I usually saved this tactic for "customers" (really they're thieves if they're not paying) that I don't mind losing, but I actually never did have anyone leave or complain about me doing this.