I just tested in my own organization, and even with the Alerting Timeout set to 120 seconds I could not replicate what you are describing using PureCloud-based stations. The agent rolls to Not Responding and the call remains in the queue.
So, it sounds to me like you are set up with Remote stations and the phones are on a different system that has its own voicemail (but that's just my guess). If that is the case, make sure the Alerting Timeout on the queue is shorter than the number of seconds before the other system rolls to voicemail.