Unfair charges for unused my o2 line while abroad

[Sami]

I was away out side the EU area over the last several months. I had opened my O2 phone few times just to get numbers from the phone and to check a message was sent to me.Although I made sure that the mobile data is off and I was only using the Wi Fi unfortunately I was charges for sending international message. I am sure I did not send any messages.

[MI5 · Accepted solution]

@Sami 

If you have an iPhone or an Android phone with visual voicemail active, the phone will send silent text messages to register for services each time it is turned on.

[Sami]

Thank you for your reply. I have got iphone, How to turn this off?

[MI5]

@Sami 

You need to turn off iMessage and disable voicemail Guide: All you need to know about O2 Voicemail 901