Apple India — my mobile iphone 7 become dead

Address: Dharwad, Karnataka, 580023

I have given my iphone 7 to your authorised service center in hubli m/s F1-Info Solutions & Service pvt ltd for IOS restore dated 26/10/2019 but till now they are not given back and saying device not supporting for IOS and not working anything as its dead and they ask me to take back dead set .

I asked give me back my mobile as it is earlier condition(which was working fine) or get it updated IOS version .But they are not responding properly and just killing the day by giving false statement.

They are not intimated any clue that if IOS not supported handset may go for dead mode before taking now saying all these story.
Need immediate response for my concern else will address in consumer court .
I have all documents and voice records which is communicated with me from your service center.