Warning To Former Employee From Desisting To Use The Company Name

Well, the prime objective of any activity concerning an organisation must be to safe guard its interests and reputation. Public notices are one of the right ways to meet this objective. Wrong use of words only shows the drafter’s cultural background and a distinct bankruptcy of vocabulary. The solution, therefore, is not to avoid issuing Public Notices but to train your staff to be more objective and polite.
U K Munshi.

Its vague to me, that he was terminated and still sending your team projects from customers. If he is contacting your clients he can direct those orders to somewhere else for his benefits.
I second Sawasta Banerjee's point about the payment.
Why would he still continue to serve his ex-employer for no gains ? Unless he is trying to revive his employment contract with your firm. Is there any reason why he would do this?
Please speak to him and hear him out. Highhandedness might not be required, if you get to know his reason for being so persistent.
A new offer is difficult to land when someone becomes unemployed. You can always issue notice and warning, once you de-root his reason in the first place.
Wish you all the best !

Ukm,
Do you think putting a public notice protects or absolves you ?
This is a market where you have to cater to your customers.
If a customer claims to have paid to your former employee because he didn't know he has left and no one from the company informed him of it, do you think your having put an advt in news paper is going to help ?
You may win a court case on that ground, but the customer is not going to pay you.
Plus you will list all future sales. Unless you are lucky to have a monopoly product.
So, I still say, not a public notice but an individual intimation to each customer would be required.