Try restarting the phone. If that doesn't work. Try removing the SD card, restart the phone and reinsert the SD card. If the phone still doesn't read the data, try connecting the phone (while the SD card is still in it) to a computer via USB cord and see if the computer can access the data on the card that way. Should it not be able to, you then may want to try the card in another device and see if it is readable.
If none of this works, then your SD card may have been wiped. While there is no guaranty that you can get them back. Deleted does mean deleted. There are a few apps/programs out there that 'may' be able to help you recover the data.
A few of the programs you could try would be... DiskDigger, MobiSaver, Android-Recovery and...