It's located in the Emporium Mall. Their information number is: 662-269-1000 ext 1726 or 1727
You might have better service if you email them at:
customerservice@emporiumthailand.com They should be able to give you the Fendi boutique number directly. For some reason, the website hasn't been updated in quite a while and doesn't list any of the numbers of the boutiques.