Ph.D

You are advised to do M.Com before seeking admission in Ph.D.

Hi,
For Germany, the best way is to go through their official website as shared here:
https://www.daad.de/deutschland/studienangebote/international-programs/en/?p=d&s=kr&id=3882

The eligibility criteria of Ph.D at IGNOU is M.Phil degree/ a Masters degree in management discipline with minimum 55% (50 percent marks for SC/ ST/ PH candidates) or an equivalent grade from a university or a recognized institution of higher learning. After Ph.D from IGNOU, you are eligible for teaching job in B-schools and universities.

Kindly specify the city.

It is not a problem, combining all these pursuits. Even after joining service, you can complete your research and submission of the thesis. Such instances are in plenty. Go ahead with whatever you desire.

Following institutes offer the same course:
University of Delhi
Indian Institute of Technology, Delhi

Hi Saurabh,
It is possible to receive a scholarship for your Ph.D programs depending on your GRE & educational scores and of course availability of grants with universities. It is worth a try.

For a regular teaching position, B.Tech is not the qualification for mathematics. You have to do PG in the same for the position of a teacher in mathematics.