EBR reporting

I have been trying for the past 2 hours with no success.

I am trying to create a simple bar graph to show:

1. How many customers each CSM has
2. How many of those customers DO NOT have an Executive Business Review logged in the past 90 days on the timeline (Milestone > Executive Business Review)

I have tried using the Activity Timeline object for this, as the Company object doesn’t seem to go into enough detail to find Milestone type. I have got as far as a table showing a list of all customers, with their CSM name, with a 0 or a 1 for EBR type in the timeline in the last 90 days. But I want something more visual and easy to see - which customers haven’t had an EBR in the past 90 days basically. 

Please help!