no such thing as a cloned sim card, to whoever said that. the usage was made on your mobile phone and yes most likely you did use that ammount of internet usage. o2 will not simply charge you for high internet usage that you have not used. the purpose of a contract is to self manage your own usage, and o2 provides you with tools in order to do that, for example going online to check your unbilled usage or by calling o2 cust service to see what you have used in charges or by using o2's 21202 text balance service. i really do not know why seeking legal advice is going to help you? at the end of the day, you entered into a contract with o2, and any usage that is not covered under your monthly allowance, you will be liable for charges. if you are going to have difficulty in paying your bills then you should consider asking o2 to help you set up a payment plan, however this will affect your credit file. if the debt is not paid to o2 and line is disconnected then the debt will be sold and transferred to a 3rd party collection agency who will then chase you up for the debt. i know this is something you do not want to hear, however your best option will be to set up a payment plan.