Thanks for your support. We ended up by paying the ransom as the only solution to recover some important files (for an unknown reason have not been backed up). We paid 0.1 BTC and they sent us a program called "Smart Descrypter.exe". Once you run it, it properly scans hard disks seeking for the encrypted files but when you try to decrypt, it asks for an Activation Code.
Let me know if it helps in any sense.
For your reference:
encrypted sample files: Encrypted.rar
resulting decrypted sample file (they did it as a free sample): Decrypted.rar