No. No they cannot. Not yet, at least.
Let’s start off by saying that no VPN service can ever guarantee your anonymity 100%. That said, there is good reason to believe that the most secure encryption schemes are nearly impossible to crack.
In theory, however, there’s always a possibility that certain agencies are operating several steps ahead of the game. For example, the NSA and others might be capable of cracking more advanced encryptions when data streams are stored for future decoding.