Does Disney Upgrade tickets over the phone?

I just got duped with my ticket from a 3rd party seller (seemed like more days than it actually was). I need to add one day ticket to my 7 day park hopper. Will disney do this over the phone? I dont want to wait for the gate because i’ll loose FPP

I had to add a day once I got there (guest services).

Did you try working with Park Savers? These ticket agencies generally have pretty good customer service. They might be willing to let you apply what you paid towards an 8 day ticket.