If you are not bothered, you can choose to manually delete the voicemail on your Motorola Moto G.
There are numerous programs available online that can recover lost data from Android phones . Therefore, if you want to delete everything from your Motorola phone permanently, you need to use Android Data Eraser, which is a powerful application to erase all data from your phone and make sure nothing can be recovered. It will erase voicemail at one shot. So, you are suggested to make a backup of your Android phone before using this software