lodge a report to your nearest police station. reason: one to be safe on your side as your sim may be used to any illegal work and you will be catch by police as the sim registered under your name. second, as soon as you reported to the police they will report and coordinate this to QTEL. QTEL has a system that can track your mobile even if they used another sim for as long as the phone is used within Qatar only. Once they have track it police will call that no. who has used your phone. Hope your phone will be return the soonest.