No response on excessive data costs

Despite numerous mails to enquire why my data costs have suddenly after more than a year trippled I get no response. Every month I simply have to cough up the money for the data usage but no one gets back to me on what is going on on my account. For all I know someone could have hacked into my wifi or 3G but have not way of tracing where the problem is. What poor service! This after putting up the contract costs without notification.<br> I've been forced to upgrade so that I could take a different contract that allows me to put a soft lock on the usage as they are not helping me to trace the source. Unacceptable