Collection options

First, next time, don't wait 90 days to do these following things.

Let's assume you've already delivered the standard past-due notices in writing and by phone, without success. Then next, arrange a face-to-face meeting, if the company is close enough to you. If it's a small business, meet with the owner. If it's a larger business, meet with the highest level person you can.

Explain what has happened, note how you've already sent several notices requesting payment, and again ask for payment. If you have a contract, bring it with you. And be prepared to prove that you completed the work or made the delivery as specified. If you have emails noting how the client has been satisfied to date with your work, bring those as well.

If the client refuses to meet with you, and still refuses to pay, you have no choice but to consult with an attorney. The attorney probably will send a stern letter demanding payment immediately and threatening further legal action. Your attorney will help you decide what to do next.