KPI for Unique Callers

My organization runs a small call center for one of our programs. I have set up a dashboard to monitor this call queue and I am trying to set a KPI for 'Unique Callers'. I have noticed that many callers will call 4+ times for a few seconds before waiting in a queue for a few minutes. I can filter out the calls that are 'x' amount of time but it would be nice to see total unique compared to total called. Curious if anyone has figured out a way to do this?