Uber Cabs - Uber driver did not return my phone

I took a ride from uber on ** June **** from Salt Lake, Kolkata at *:** p.m. and reached Birla Planetarium at *:** p.m. But unfortunately, I left my Asus Zenfone Max cell phone inside the cab. After ** minutes I realised that the phone is not with me. So I made a call to the number which I have lost. The uber driver received the phone call and told me to stand on the location so that he can return it to me. After waiting for ** minutes I again called my number, but then it was switched off. So I call the driver through the uber app. The driver again received the call but denied the fact totally. I repeatedly asked uber to provide me with the number of the car. But they did not provide any data about the car as well as the driver. Being a medical student I have a lot of data about the patients and many valuable books inside the phone. But now I have lost everything just because of the poor response of uber.