How can I permanently delete deleted calls and messages

Hello Amylouiseaicha,

When you Delete messages on iPhone & View and delete the call history on your iPhone they're permanently deleted unless stored in iCloud or in a device backup.

If you don't want calls to sync with iCloud, you can disable iCloud Drive. If you don't want messages to sync, turn off Messages in iCloud. Turn iCloud features on or off - Apple Support

If you'd like to delete an old backup, check this out: Locate backups of your iPhone, iPad, and iPod touch

Cheers!