un authorized payments

Hi,

i checked my phone bill and someone has used my son's phone number to purchase stuff from Microsoft.

Both myself and my son hasnt given anyone permission to do this. I called my phone provider and they have told me to get in contact with Microsoft to get the matter sorted as i cant afford the £235 something they have spent.

There is nothing on my Microsoft account about these purchases and everything ive done to contact someone about this, is just drawing a blank.

regards

Rob

:)