How can I decrypt my photographs on the SD card? My Samsung Galaxy S3 crashed suddenly and I had to take my SD card out to fix it. 

After I got it back and put my SD card into it, I realized that the data which was encrypted on my SD card (photos of my son) are unavailable to view. The files appear broken. I tried to encrypt my phone again with the same password, but it has not helped.

How can I access my files/photos again?
It sounds like the service center did a factory reset, which means you should not be able to recover the contents of the SD card. It's designed that way and is a good thing as it protects data being read if your phone has been lost or stolen. 

Any chance you have backups (on your desktop? google drive? samsung’s backup site?)?