Should you send a Demand Letter yourself or through a lawyer when the other party is in breach of the contract?

You entered into a software development contract with a software developer in Pakistan and he failed to complete the work and/or to conform to the project requirements.  The developer is now not even responding to your phone calls or emails. Should you threaten the developer with legal proceedings yourself via an email or hire a lawyer in Pakistan to send a Legal Notice/Demand Letter? It is entirely up to you. There is no mandatory requirement of sending a formal legal notice through a lawyer but the developer may take the lawyer’s notice/letter more seriously.