I have someone harassing me for about 5 years now.  You cannot block such users from leaving VMs.  In the past year, Koodo increased the maximum length of message to 5 minutes with no adjustment.  I require this to be set down to 15 seconds - there is no reason anybody ever needs to leave a message longer than 15 seconds.

I have found that Rogers lets you set it to 30 seconds - if Koodo doesn’t offer the same alternative, I will drop my Koodo account and switch to Rogers.