Use occ and its file decryption features without direct access to occ

I'm currently using the latest ownCloud release and so far, everything's been okay. Except for that the entire cloud suddenly stopped working (Error 500 after some time trying to connect to it, neither App or Desktop client could connect to), which is one thing. However, I got my files (merely important...) encrypted there. Now that I can't any access the normal ownCloud web interface, I need my wife's and my data back decrypted. However, occ is simply not working. I actually spent hours trying to get it to work again, nothing helps. So, occ is definitely out for this one.

I still got all the files on the server, and now I need to decrypt them. Any ideas?

occ isn't working, what errors ? what OC version ?