I think this is a known issue/bug when booking on Delta.com.

I booked a one-way flight for three people like normal and everything goes through fine and I get my confirmation email. A couple weeks later as I review my credit card statement, I noticed 9 charges and not the usual three I would expect (charge per ticket).

I searched for MyFlights (https://www.delta.com/mytrips/findPnr.action) using my credit card # and name and found the same itinerary with three different confirmation numbers. I only received one of the three confirmation numbers via email.

I called Delta (800-221-1212) and was forwarded to their refund department and the representative understood what had happened immediately and said multiple reservations and charges are sometimes known to happen and it is a bug they're working on. She spent about 20 minutes refunding me for the duplicate confirmations. The MyFlights website didn't show the duplicate confirmations. I am waiting on the refunds to be reflected on my CC statement.

Not sure if this happened because I booked a partner airline (WestJet) on Delta. Anyway, double check your credit card statement folks!