First, set up a record selection formula that limits the date field:
{table.date} in dateadd("m",-12, currentdate-day(currentdate)+1) to currentdate-day(currentdate)
Insert a group#1 on customer and then a group#2 on date (on change of day)--they must be in this order. Then go to report->selection formula->GROUP and enter:
distinctcount({table.ticketID},{table.date}) > 1
-LB