Hello!
My previous post was moved to accepted bugs. But another player had solved the mistery for me. Interesting though that a player found out the solution to my problem that the support team did not. In short, I just had to found out a NPC called calamity salvager, and there was my chocobo whistle and Gobbue horn. I retrieved it, used it, and finally have my mount! Thank you for your attention! Tried to reply this solution in my previous post, but did not have permission to.