Pipedrive doesn't aggregate activities at a particular level, yet.
As a workaround, you can create a new activity type, and at the 3rd failed attempt, create an activity with this new activity type.
You can create an automation to send an email, and mark this activity as done, whenever this activity is created.
Hi @Martin Pavion
Why wait? What we do is send an email immediately after an unanswered telephone call with the reason for calling and when we will call again. The conversion then flies up.