Check your Ticketmaster account if you purchased tickets between 1999 and 2013.

There was a class action lawsuit regarding their fees and anyone affected was given a voucher good for a set of tickets to an eligible event.

Log into your account, click '[your name]'s account' and click on active vouchers to see what you have.
I got two sets of tickets. Oh, the voucher is good until 2020.

Here is more details on it.\

How many vouchers did you have?