Playing sounds using WTV020SD mini
Im using a piezo speaker. Did i do something wrong? 


The diagram shows an 8 ohm speaker. Piezo speakers are capacitive and have a higher impedance.



It may be best to get the module working by itself first



As your  link says


The SD card must be FAT32 formatted.
The audio files must be encoded in 4-bit ADPCM.
The audio files must have a '.ad4' filename extension.
the filenames must be 0000.ad4 through 0511.ad4.
the files must be in the root directory of the SD card not inside folders.
you should probably have nothing else stored on the SD card.