Well not much to go there.. I take it you have tried the obvious ansa of call it and see if anyone ansas.....
O2 won't be able to trace the phone, but depending if your Android or iPhone, these links might help :
If an Android use https://www.google.com/android/find
If iPhone - use iCloud and find my phone - I used this method when I lost my iPhone.. and found it about 2 miles down the road! 😅
Crown Communication - an O2 Select Partner
