First, when did they tell you payment would be made? Always be polite. When your inquiries are ignored, contact Title & let them know you've not been paid as Title will most likely put some pressure on hiring party.
Obviously. stop taking work from non/slow payers, Some notaries go so far as to fill out a small claims form and send it to non-paying co. with a statement that if payment is not received by (a reasonable future date), this will be filed. I've never had to do that so don't really know how effective it is. Another is to say you will post of this non-payment everywhere. Again, don't know how effective that is. Most important is to just nag the daylights out of them and never, ever just accept the loss or work for them again.