@zhejunli
SMS content is autologged by the network's SMSC machinery and carriers are required (by the CRTC) to retain that data for "3-5 days". Although Telus is known to retain that data for at least "30 rolling days". And some carriers are known to archive their user logs indefinitely or forever - every communication ever sent over AT&T USA network since 1987 has been saved. Though anything they've retained beyond the legally required period is essentially their private property, they don't have to provide it on request (for legal warrants, police requests, and government or industry inspections), they don't even have to admit they still have it. (If this bothers you, then look at encryption apps like Signal SMS.)
But such data are usually not saved in human-readable formats. And obtaining a copy is basically impossible for normal subscribers.
https://productioncommunity.publicmobile.ca/t5/Get-Support/Text-message-content-retention-R-v-Telus/...
Apple iCloud subscribers can retrieve their entire iMessage library by signing onto any iOS device. Samsung, Google, Microsoft, Amazon, Huawei, and others each have their own counterparts - although these require you backup your messages beforehand.
The short version is that if you don't still have the phone these messages were stored on and you don't still have a backup of these messages (somewhere on the cloud, a SIM card, or a computer drive) then they're basically gone forever and you'll never see them again.
