Unable to select or upload new ringtone from local device using Themes

I am trying to change my ringtone for Task remainder application from notifications panel. On clicking choose from local ringtone it display me some black screen and on the top saying "Add Notification". Later I opened themes app and decided upload new ringtone for local ringtones by click "+" button on bottom right, then it says "Select Tone" with black screen again.

I uninstalled which broke my phone like I couldn't even select ringtone from locals too, and my phone keeps on asking to report bug when I was trying to change the ringtone.

I later restored it and even updated to latest version. And I even tried to change regions on my phone.

Can anyone help me with this situation?