Hello Jatinder,

The best university for pursuing maths as well as economics honours is-

Delhi university

It is the most reputed institution of India and some of it's college are really popular in the country,  most of the North campus colleges are best. For mathematics honors,  the following colleges are best..

1) Hindu college

2) Hansraj college

3) St. Stephens college

4)  Ramjas college

5) Kirori Mal College

6) Lady Sree Ram College( All girls college)

7) Shri Ram College of commerce

8) Venkateshwara College, south campus

The University of Delhi will begin the DU 2020 admission process from the first week of April with the release of application form at UG admission portal du.ac.in.

IIT Kanpur, Kharagpur are some of the IITs that offers the economics honours.

Good luck,

Hope it helps :)