Joining A Competitor

Hi I have received a letter from my company stating that I have joined my competitor and they would be taking a legal action against me if I dont respond with a reason so as to why have I joined the competitor. I have already received my reliving letter and experience letter from the company.
The offer letter that I signed had a clause that I cannot join a competitor for a period of 1 year Can the company file a case against me and what would be their course of action. I letter that I have received is on the company letter head.
As far as I know it is constitutional right of a person under section 27 to work for any company.
I just wanted to understand that can I take a action against the company as well cos they are threatening me by filing a complaint against me which is against law. Can you please advice.

Please review below topics, you can have an idea..
https://www.citehr.com/180299-joinin...r-company.html
https://www.citehr.com/289258-joining-competitor.html
https://www.citehr.com/343871-restri...ompetitor.html
Thanks,

Thanks a lot for your help Mr Sayeed.
Just had one more question as the company has sent me an letter on the Company letter head asking for details should I respond to the letter or completely forget about it and do my work as usual.
What would you advice as an further course of action.