Did you receive a call from any numbers which begin with +234 or +372?
Our suggestion is to never answer it.
Especially if you don’t have any families or friends living in those countries.
There is no reason to pick up the call or to call them back.
This kind of call is known as Wangiri (literally one ring and cut) Fraud.
Originated from Japan, this fraud involves fraudsters leaving missed calls from unknown numbers on your phone and if you call them back, your credit will be drained or your bill will be charged.
Recently, there have been some foreigners in Japan who received these kind of missed calls. Sometimes the call gets disconnected and sometimes it rings longer.
If you call them back or pick up the phone, you will hear some sound asking you to stay longer on the phone such as an operator saying “All operators are busy at present, please hold”. It is also possible that you will hear nothing.
What you need to do is to just ignore the calls.
Hope this helps
Enjoy your stay in Japan!