Hi and Welcome. My Name is ***** ***** I look forward to assisting you today with your question.
As you probably already know, when you delete something from your phone, only the reference to that file is being deleted and the actual file will be still there for a limited time and could be recovered using third party data recovery applications. These deleted files or items will be there until they are over written with new ones. It is possible to retrieve deleted files like messages. But that completely depends up on how much you used your phone after you deleted them.
If you have taken photos or videos, downloaded apps, received/sent multiple messages etc after you deleted them then the chance of them getting recovered is slim to none. Because they might be over written with new ones.
The more you use the phone, the more it become hard to recover. However, you can attempt to recover them using the following applications
Dr.Fone for Android from Wondershare --> https://www.wondershare.com/data-recovery/android-data-recovery.html
EaseUs --> http://www.easeus.com/android-data-recovery-software/free-android-data-recovery.html
The application are paid ones, so try the trial versions before buying it. Again, I can't guarantee they can be recovered. If you are unable to recover them, please don't rate me bad or poor as this is something I can only give instructions on and the success completely depends up on the factors I mentioned.
There is also another way. If you have a iCloud backup prior to the deleted date, then you can restore to that backup point. Go to Settings > iCloud. Tap Backup and check the backup date of your iPhone. If it was before deleted date, then you can erase your iPhone and restore to that backup.
I must warn you, when you restore to that backup, everything since that backup will be deleted from iPhone (like contacts, photos etc) and only the stuffs until that backup will be restored on your iPhone. So only restore to that backup if it is really important.
If you have any questions or would like any additional information, please don't hesitate to ask.