HTC /S720
Phone Gets Off

I have purchased HTC S720 in last June. It worked for 7 months but since than started giving problem like

1.) It hangs.

2.) Internet is always on even you disconnect mounting lots of Data Usage Charges

3.) Go off in when you talk for 2 mins and will switch on only after few mins. However, works ok with charger connected to it. It is not a battery problem.

Most pathetic phone and service..

Regds