Dear Karthikeyan,
Every company has Industrial Standing Orders approved by the labour department. In the standing orders, misconducts are well defined. Please check the standing orders and find out whether downloading a third-party app is misconduct. If yes, then the company is empowered to take action against the defaulting employee.
Definition of misconduct apart, the company must conduct a domestic enquiry. The enquiry must be conducted as per the procedure and if the blameworthiness of the employee is established, then only the company can award a suitable punishment which could be the termination from employment also.
In your case did the company conduct a domestic enquiry?
Thanks,
Dinesh Divekar