There is one thing you can do, but it is purely theoretical. If you haven't removed the virus, you can try sniffing out the traffic from the infection file to hopefully find the decryption key while it is being sent to cyber-criminals. Here is more info on this:http://sensorstechforum.com/find-decryption-key-files-encrypted-ransomware/
The downside of this method is that you have to be infected with Cerber and know how to sniff network traffic. Another downside is that the traffic is usually encoded in another format and even if there is a key, the cyber-criminals may have thought about obfuscating that as well.
Another method that you can attempt is try absolutely every single decryptor. But to do this you have to copy the encrypted files to a flash drive for example and test decryption tools only on copied files, because they may break the files indefinitely in case you are attempting to tamper with their structure (like a trap). Here are some free decryption tools and do not use them on the original files, please:http://support.kaspersky.com/viruses/utilityhttps://decrypter.emsisoft.com/
There is also another option, but I am not sure that it can work. If you know what System Restore is and if you have set restore points on earlier time on your computer, you could attempt to restore it back to before the infection, but bear in mind that everything you have done after the infection may dissappear, so back it up. Technically System Restore only restores certain aspects of your PC, but not all of it. I am not sure but if your files are encrypted, they theoretically have modified settings on them. If System Restore brings back the old configuration and settings before the encryption(If you have set a restore point), you may succeed in restoring some documents. Here is full info on system restore thanks to howtogeek.com:https://www.howtogeek.com/howto/windows-vista/using-windows-vista-system-restore/
Other than that, our team is actively researching for a universal solution against this problem, besides backup and we are yet to find one.
By the way, in the future, if you see malicious e-mails please check the attachments before opening them online. Here is one website that can help you with that:
Before you open an attachment next time, simply upload it on this site. If it detects a virus, do not open the attachment. This is a very good and free way to protect yourself, but you have to make it your habit.
Best Regards and best of luck,