In a 5 day trip to New York my phone ran up 15 times my normal

Yes they are. The main issue here is that you have final responsibility over how the phone is used and the data coverage you use whilst abroad. Whilst data coverage is capped when you travel to European countries, that does not apply to usage outside of the EU so your trip would not have been protected by a data cap. This means that you could run up an infinitely high bill, depending on how much you used your phone whilst abroad. If you did not understand the instructions on using the phone properly or it was your error that resulted in you using data roaming rather than wifi then that is not the mobile provider’s fault so you cannot really hold them liable. If they can show that data usage abroad was used by you and it was charged at their standard rates as communicated to you in their terms and conditions then you could be liable for these. The fact that you may not have set your phone settings correctly, assumed you were not using data when you were or it was playing up would not make them liable for these charges. Also they are not automatically going to be required to stop roaming if it appears your bill is becoming excessive. Had you advised them of a specific cap in advance and they failed to stop the services or send a reminder then you could hold them liable but they do not automatically alert every single user who starts spending more than usual whilst abroad, especially as there are many users (usually on business) who would run up large bills. So if you did not cap your usage, it was your fault that the mobile phone used data roaming rather than wifi and no fault can be placed on the provider, then it would be rather difficult to get them to reduce the bill. You have to show fault on their part for that to happen. You have nothing to lose by raising this issue directly with them and would be expected to complete their internal complaints process before you can take it any further. If your service provider decides not to refund you, and you feel that the charges really are unfair, or were not made clear, you can take your complaint to an Alternative Dispute Resolution scheme – either CICAS or the Ombudsman Services: Communications. A step by step guide on how to approach this can be found here: http://www.which.co.uk/consumer-rights/action/how-to-complain-to-the-ombudsman-about-a-mobile-phone-provider I trust this has answered your query. I would be grateful if you could please take a second to leave a positive rating (selecting 3, 4 or 5 starts at the top of the page). If for any reason you are unhappy with my response or if you need me to clarify anything before you go - please get back to me on here and I will assist further as best as I can. Thank you