I've just registered to thank you. This really had helped. I didn't have compressed air, so I just have blown through a napkin with my mouth. I couldn't find the solution of this problem in Russian Internet.
Thank you, good man!
I just wanna note. Blowing up didn't work for me. Just simple instructions from here https://forum.xda-developers.com/showthread.php?t=2771972 helped me. But the file "/efs/prox_cal" didn't exist on my firmware and I created one with the command "echo -en $'\x96' > /efs/prox_cal". So, now in test mode (*#0*#) I see the high value 255 and the low value about 150 and the proximity sensor works!