Caller: I don't know

Called, left no voicemail, when you ring back it has a fake "this number is not in service" recording.

No message left - called number back (anonymously) and got a message with an unusual accent “The number you have dialled is not in service - please check the number and call back later”. Definitely suspicious.

Sorry, we previously entry may not be accurate: no voice message was received instead.

The voice message came with background noise.