There is an employee named Matthias who wrote
[quote=“Matthias_Quellmann, post:9, topic:780485”]
You can tag me in your post if you want to increase the chance that I read it.
[/quote] ,
he may be able to help as well (to tag in this forum, type " @xyz" , where xyz is the exact spelling of the forum name).
I am from India
You can’t activate Cubase 11 if you don’t own a license for Cubase 11.
This is how I understand it, but like @skijumptoes and @alexis just wrote, try and contact Steinberg support or Matthias. None of us work for Steinberg.
I am from near Hoboken.
(Sorry, I couldn’t resist) 
The official distributor and support address for India is (according to Become a Steinberg Reseller | Steinberg) Yamaha:
Contact them and try the other suggestions. Noone outside Steinberg and its designated affiliates can help you with your request. You need a license for Cubase <=11, which you did not buy.
I do not understand, why you did not buy Cubase 11 before 12 was released. Steinberg communicated the change including the licensing long beforehand. There was even a long grace period. You had enough time to get it if you wanted it - and not 12. Why don’t you work with 12 if you got it?
Cheers.
