I believe the only way of finding this out is, if the texts are scary or offensive or threateneing, to report them to your local police station, and then the police contact your service provider to ask them to search for the information. It's best if you also ask them and give them you crime reference number. Your Service Provider cannot offer this service to you-they will only do this if asked to by the police. I have been advised it can take up to 3 months.