Welcome to FT, Minny P, and sorry that it's happened to you.
While I don't have any specific recommendations for you in this regard, if you don't get anywhere with Expedia, I would just dispute the charge of the first flight with your CC, noting that the dates of when you first booked the transaction and the date on the confirmation. They should be able to get it straightened out for you satisfactorily.
Good luck, and let us know how it goes!