If I can't resolve a ticket refund issue (ticket was not honored because of a computer thing) with the airline or PayPal (more than 45 days) who else can help me with the dispute? FAA or small claims court or anyone else?

I purchased a Qatar Airways ticket to Pakistan. I then changed the dates 2 weeks prior to departure and paid the change of ticket fee. I received a confirmation. I called the service center ahead of time to confirm that the reservation was changed and received affirmation. On return from Pakistan, they the agent said that my reservation was not changed and I had to purchase a new return ticket. Now when I check with the airline they say that the change was not done as the credit card did not accept the charge for the change fee. And that an email had been sent 2 weeks prior to my departure. They will not accept my argument that their customer service confirmed the change on the day of travel.
If I cannot resolve this with the airline who can help me resolve this? Can I take to a court or FAA or some other customer agency?