my account got hacked and my gil was stolen

Date & Time:
Frequency:
World name: malboro
Character name: Terranort Terumi
Retainer name: Flaky
Class/Level: GNB lv80
Area and coordinates:
Housing: mist
Steps:
1. for accident enter a link to enter the forum wich is false
2. two days later i enter the game and for some reason i appeared on ul dah, near the aetheryte, also with 900k gil on my character (i had around 20k on my character last time i logged out)
3. checked my retainer called flaky to check the missions as usual and wanted to save the extra gil, but when i was about to do it the 17 million gil i had stored on her was gone

this isn't a bug you need to contact Square Enix support. the GM's here nor the ones in game can help you.

also, they won't be able to return your gil.

This was a phishing link and they warn about it all the time, there are several threads about this as well...

I'm sorry this happened to you. My advice is to never visit links from people who send a tell out of the blue. Even people you do know may have been hacked too, so inspect the link carefully and make sure it's authentic. The scam ones have a different extension than .com, so verifying these little parts of the address are consistent with the real website is important if you deem it worth your time visiting a link at all.

In a similar situation, you could navigate to this forum yourself and find the real thread yourself, rather than pasting what could possibly be a malicious link.