Hello Nurseupi,
Welcome to the community!
Unfortunately, the mobile providers do not keep a record of sent text messages. The messages are only stored temporarily on the SMS message centre's servers until delivered. If undeliverable, the messages will automatically be deleted from the servers after the validity period has elasped (see here and here). Typically, the validity period is only a couple of days. Unless you manually backed up the messages on your device and you no longer have the messages on your device, there is unfortunately no way to retrieve them.
Not what you wanted to hear, but hope this helps 😀
Cheers
