Virtual Gift Card

I traded in my I Phone for a $330 Virtual gift card. I go to use it to pay my bill and it doesn't work. I am being told the PIN is wrong.  I have spent over 4 hours with customer service to only be transferred to over 10 different departments. This is insane and unacceptable.  I need assistance here as i see online that this has happened to many people over the years.  For the amount i pay each month for service, this is unacceptable.