Lost mail

I used postnet at Brooklyn mall to send very personal mail on the 18th of February 2019. I had a deadline to meet and my ID documents, bank details etc were contained in the mail. I used their fast mail service with the promise that it would reach the intended destination within 3 days. It's now been 7 days and my mail appears to have beeb lost. The excuse I'm given is that it can't be tracked because it's fast mail. Never mind that i have paid for a service they claimed they could provide. I am so angry about their disgusting service.