Charges while abroad

[Class2ldn]

Hi all, currently in Cape verde and have just seen I've been nearly £28 for my first day here and 81p for the 2nd day even though I've had all my mobile data and data roaming switched off. I got the usual here is your charges text and then immediately switched off data and roaming. Theres no way in about 20 minutes from getting off the plane to switching it all off I could accrue that amount of charges.
Spoke to someone on chat who tried saying that's how my phone is designed and that even though I have all data etc switched off it can still use it which is rubbish.
Offered £10 refund which is a joke.
Any ideas how I could have been getting data through or where to go next with this as it's a disgrace?

[MI5 · Accepted solution]

@Class2ldn 

At over £7 per mb it's very easy to use £28 worth - only 4mb!

Also if you turn phone off it can use small amounts of data when you turn it on even with data turned off.

The best thing to do is leave it on airplane mode with wifi on so you can use any hotspots when you find them.

[Bambino]

@Class2ldn  Put your phone in airplane mode and use WiFi wherever you can.

[Class2ldn]

Thanks for the advice but how is my phone still using data? Also I didn't use my phones internet at all after landing and before I had switched the data and roaming off and have only been using wifi.
My phone hasn't been switched off either

[MI5]

@Class2ldn 

Are you using airplane mode as I suggested?

There's always a risk if not and 81p is literally a kB or two.

[Bambino]

@Class2ldn You may have only switched off roaming, but your mobile data may have still been on. It's easily done, and can wind up being very costly. Use WhatsApp over WiFi for calls and texts if you and your contacts have the app. Won't cost you a penny.

[gmarkj]

Do you have an iphone?
Turning it off/on causes imessaging to use a little bit of data to register before wifi kicks in.

[liggerz87]

It's also worth turning off voice mail as that can charge you