Apple didn't auto-delete your messages. By your own admission, you had the setting set to auto-delete them. Unfortunately, once deleted, they are gone. If you don't want messages to auto-delete, change the setting to Forever.
It would be possible to get messages back IF you don't sync messages with iCloud and you have backups from before your messages deleted. But the issue with that is when you restore your iPhone from a backup which may have those messages, your iPhone will be restored to the date of that backup. This means messages received AFTER that date will be gone. So there really is no solution which is optimal except to never have messages auto-delete going forward.