We found some customers often forget to turn on roaming for certain sims, or their phone is locked to a certain network (e.g. Telstra or Optus), hence they have problem using the sim. Please always contact us as soon as you find there is a problem when you are overseas using the sim, we will always try to resolve the problem together. We do not accept return / refund if you only contact us after your trip / when you return to Australia.