You are on the right track, that will give you the max call datetime per account and user. What you need to do next is create another calclulated field and it should look like
[Max Call Date] = [Call Date]
Then apply this to the filter to get just the last call for each user.
Next, you will need another calculation
datediff('day',[Max Call Date],today()) > 30
then apply that as a filter as well to show only those over 30 days.
Which Column will you use to find Maximum Date? and Are you Trying to Find with Reference to Today's Date?