Data off when screen locks. Huawei P20 Pro

Hi guys. I am trying to set up my phone to switch off data when phone screen locks. In the Huawei P20 Pro under battery options there is an option "Connection when screen locks" with 2 options: keep wifi on and keep mobile data on. For both these options I have selected switch off.

I would expect that the device now does exactly what I want it to do, namely switch off data when phone screen locks. However I tested if it really works by sending an email to my phone from another device while the screen was switched off and alas, the data is not switched off.

Any other Huawei owners experiencing similar issues? I would really like to be able to switch off data when phone screen locks. Thanks for any suggestions.

Maybe it makes an exception when you send an email or only switches off data after a few seconds? Try to see if you can turn on screen lock data usage, it'll tell you how much data is used when the screen is off, if the figure isn't zero/close to zero then data is on.