Flipkart — Replacement problem against a defective mobile phone.

I purchased a Relame Narzo 20 (order ID- OD[protected] on 16th January and delivered by the flipkart on 17th January . Since then the fingerprint sensor is not working properly. As a result I'm facing a lot of problems as I'm a headmistress of renowned institution.
I requested to the authority to replace the phone or to fix the problem. In reply, technician (Mr. Snehamay Samanta, ph no - [protected]) visited my house on date to solve my problem but he could not and not only that he behaved rudely and the authority rejected my return request.
Therefore, I solicit your kind intervention to solve the problem as early as possible and save me from harrasment.