Proximity sensor XZ locks phone every time you pass over it

[Redtembo]

Think I may be in the wrong place so apologies if so. I have a Sony Xperia XZ and it is driving me mad. The proximity sensor seems faulty as it will suddenly return the phone to lock screen when you are in the middle of browsing/using apps/general use. It seems to be when you pass over the proximity sensor on the front

[Marino.Manolo]

Will it not be the fault of a film on the display?

[Redtembo]

There isn't a film, no screen protector of any kind. When I go into the service menu it says the proximity switch is off but you can't turn it on again.