Mai bsc mathematics karna chahta hun but collage nahi Mila so kya bTech me aisa koi course hai.
Well as the name days B-TECH means bachelor in technology. So their is no course like in which you can do mathematics only. Every stream have some technology involved with it and in those technology you can find some mathematics part like in mechanical, aeronotical, aerospace and all the branches have a little bit of mathematics involved in them. So their is no branch like in which you have mathematics only.
https://engineering.careers360.com/colleges/list-of-mathematics-and-computing-engineering-colleges-in-india