Employee Poaching by Direct Clients

One of my former employees has joined a new company that is founded by the directors of a direct client to my IT services company. This new company is developing the same software that my company was contracted to build, and the employee who has moved there was actually involved in the software's development while working for me. The contract completed and both companies part ways but they "Poached" my employee and hired them under the newly registered Pvt Ltd fir,. When I brought up the matter in a formal email to the client's directors, they assured me that they haven't hired anyone from my original company without my consent. However, it appears that this new company they've established has indeed recruited my former employee. Given this, I'm concerned about the legality of the situation and the possibility of them recruiting more of my employees in the future. All of my employees, including the one who left, have signed a non-competition agreement. The clause states: "You agree that for the duration of your employment, and for twelve months after its termination for any reason, you will not solicit or attempt to solicit business from any customers, prospects, or vendors with whom you had substantial contact during your employment with us." Employee left us 2 months back only. I'm looking for advice on how to proceed in this complicated situation.