You should prepare for JAM Examination in Maths followed by Admission in IITs, NITs in M.Sc. in Mathematics. The Institutes have excellent infrastructure, faculty and research facilities. Besides them, you may also consider Postgraduation from Public or Private Universities.

For more information about M.Sc. Mathematics and Colleges do follow the link below

https://university.careers360.com/colleges/list-of-msc-in-mathematics-universities-in-india

For more information about IIT JAM Examination do follow the link below

https://university.careers360.com/articles/jam

If you want to study Mathematics then you can go for-

1. M.Math course in ISI. It will be a great research based course which you can enquire in the website.
2. IISc gives IPhD options on the basis of JAM/JEST exam.
3. By attempting IITJAM you can go for different IIT's,NIT's.
4. You can go for CMI for Mathematics.

Enquire about all of this courses. These are one of the great Mathematics institutions.

I hope my answer helps. All the very best for your future endeavors!