So you have an iPhone, but you don't want to use it overseas. What do you do? Simple, you switch off roaming. But that's not stopped the charges coming in for some users.According to the Daily Telegraph, some iPhone users have complained to moneysavingexpert.com that they have been sent bills of overseas data use despite having 'roaming' switched off. One user even got back from a US holiday to face a £1,500 charge.Most users have been refunded when the charges were challenged, charges that have been levied by all networks, although the majority have been from O2. Speaking about the proble, Martin Lewis of MoneySavingExpert.com, said: 'Those who have paid when they shouldn't have, should contact their network immediately and demand a refund. In some cases, we're hearing the networks are paying out without too much argument, which could indicate this is a known problem. Let's hope it does not get brushed under the carpet.'The website advises that you make sure your phone software is up-to-date, data roaming is switched before leaving the UK and emails are set only to retrieve manually. EU charges for data are now capped (unless you request otherwise), but if you are outside the EU, this isn't the case.