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Big daddy resolved it 
You have to sacrifice resetting the phone using the Sony PC software 1st. Avoid data backup from old accounts.
Then, after the reboot is done and Android is reinstalled with update x.x.x.534 goto the dialer & type *#*#7378423#*#* then press dial
In the menu that will come go to calibration and then choose proximity sensor. (If you run the test it might give error = -1) Then, set settings to default and it may ask to reboot the device.
After reboot type *#*#7378423#*#* then press dial. In the menu that will come go to calibration and then choose proximity sensor do the test and it will show success. VIOLAAAaaaa!!!!
Check the phone...it works 
Have tested this and the issue is resolved on my phone finally ....yippieeeeeee!!!
Clever!! Although I don't have this problem, but thanks for sharing!!
Thank you so much!!!! It worked!!!!! ❤️ i was so depressed , thanks a lot dude ❤️
Thanks a lot for this fix ....it really helped me a lot....
I owe you a beer.....:smileycool:
finally my problem is solved
many thanks
cheers 
looks more like a software glitch to me. gets resolved after these steps as confirmed. Plz dnt 4gt to give kudos 
Hi can I restore using phone settings and complete the remaining steps please tell me.
@phantomrocks wrote:looks more like a software glitch to me. gets resolved after these steps as confirmed. Plz dnt 4gt to give kudos
This is not a hardware problem right??:seismology's: