If you have your iCloud backing up your iPhone (or you are choosing to still back up via computer) and the deleted text messages were packed up prior to your deleting them then you can restore your device from that backup and retrieve them. Otherwise, they are gone if you deleted them.
So sorry if you are having trouble retrieving deleted text messages from your iPhone! I would just like to confirm what kaebfly already mentioned, unless you had iCloud actively backing up your iPhone's data & it backed up prior to the deletions, the deleted texts would not be retrievable. I'm including a link with information from Apple regarding the backup options with iCloud here.
I hope we have answered your question, and have addressed your concern.