Lose the second paragraph of the letter. It makes it sound like you are begging. Shorten and tighten the verbiage, and make it directly to the point. Delinquent clients rarely read a demand letter to conclusion. They know they are delinquent. They know the amount they owe you. As soon as they realize that it is a demand letter , it goes into the waste can. However, in most states you are required to make demand for payment before going to collection.

Send the letter certified mail return receipt requested. The delinquent client will take it more seririously. You will also have proof that you sent the required demand for payment if you go to litigation. Give them ten days to pay you. If the client does not make payment within ten days, serve him with a summons and start litigation.