My Phone Lost Service, But My Parents Work Perfectly Fine? What Do I Do?

Have you tried a different simcard on this phone to see which of the two is faulty. If a different simcard works on this particular phone, then the problem must lie with the original simcard (to resolve this you must contact your service provider and explain your sudden loss of service). If a different simcard does not work either on this one phone then the problem should lie with the phone (to resolve this you will have to take the phone back to the shop from which you bought if it still has some warranty or take it to your nearest phone repair shop if it has no warranty any longer or cannot be taken back for some reasons.