Thank you for your references. The main clause of that agreement that I violated, according to their lawyer, was as follows:
1) "In the event the employee leaves the service of the company in breach of the agreement, he shall not serve in any capacity whatsoever or be associated with any person, firm, or company carrying on such business for the remainder of the said period (3 Years). In addition, he must pay the company as liquidated damages an amount equal to the salary the employee would have received during the period of sixty months as calculated based on the last drawn salary and shall further reimburse the company for any amount spent on training."
2) They are thinking that I have joined hands with their competitors, informing their secrets, and approaching their clients. Whereas, the truth is I have established my company on my own, and all my clients are earned through my marketing activities. My products/models are different from theirs.
3) They are claiming heavy losses and have asked me to pay 60 months' salary based on my last drawn salary. They requested the payment within 7 days, threatening to take legal action if the payment is not made. This letter was received in September 2015, and there have been no updates since.
I consulted my lawyer, and he advised me not to worry about this notice. He suggested filing a case against them for threatening me to pay the above amount and for obstructing my choice of career.
I am a startup and do not want any hassles right at the beginning of my business career. So, I am just waiting to complete the 3 years. I left that company in October 2013. This post was to clarify whether I should wait or proceed to build my business.