Recovering Erased Audio on Android cellphone
Try taking your sd card out and using recovery software like recuva on your PC... You may also take it to a professional data recovery store, but they typically charge a lot. Data recovery apps for android also exist but I cannot vouch for any... Spend your money carefully!

[EDIT] POSSIBLE SOLUTION(S):

SOLUTION ONE:

Download ES file explorer (free) on your android phone from Google Play. Search both the internal memory and SD card for the missing files... (Tip: There are plenty of tutorials on YouTube)

SOLUTION TWO:

Take your SD Card out and connect it to your computer with a SD card reader.
Use a data recovery software:

Windows:

Testdisk (FREE) [http://www.cgsecurity.org/wiki/TestDisk_Download ]
Recuva (PAID/FREE) [https://www.piriform.com/recuva ] 
GetDataBack (PAID/FREE) [https://www.runtime.org/data-recovery-software.htm ]

SOLUTION THREE:

Use data recovery apps on your phone:

Disk Digger (PAID/FREE) [https://play.google.com/store/apps/details?id=com.defianttech.diskdigger ]


SOLUTION FOUR:

Take your phone to a Data Recovery Store (CAN BE EXPENSIVE!)