Apollo Pharmacy — Poor quality of Product - pulse oximeter

I am writing to you to raise an issue about Apollo Products
product: pulse oximeter
Serial Number: 08HM225614

issue: not working properly, poor quality build, I bought this product 20 days back. reading is in pulse it's showing spo2 levels, spo2 levels also not correct.
The battery back side spring not in the correct place (+) sided we have the spring instead of (-) side I have attached photos

so wanted to replace with another brand, I asked for a replacement for pharmacy they refused to replace it, they wanted the packed cover then only they will replace. who will keep the parking covers with them? I have suggested everything noted in your system why can't you get the details in the same they have no answer.

Pharmacy details: apollo pharmacy, 7th Ave, Sarvamangala Colony, Postal Colony, West Mambalam, Chennai, Tamil Nadu 600083

How I affected?

due to Non-accurate value, scared and went to many times hospital.
My details: K Ranjith Kumar