It did happened to me.
You probably have a different IP adress, OR you cancelled your token, OR you tried to enter your account from another IP adress (friend's house, or relative's). Token is nice, since it cancels the IP adress. You can play from anywhere in the world, and SE wont care about it. Now, not using a token, and play with another IP adress, your account gets flagged and then they freeze it, until you can prove, somehow, you are the owner of your account.
What happened is that one year ago, i played the game for a few weeks. Then i quit. Then, a few weeks later, i moved to a new place. That means a new IP adress.
I finally decided to give FF14 another chance. I did try to reactivate my old account, but since i didn't remember my pssword. Since my characters weren't high levels anyway, i didn't bother trying to find my informations. I just started a new account.I did a terrible mistake. I started a new account, but with the same email i already had given to SE for my old account. So both, my old and new account, were linked. BUT, for SE, both account have 2 different IPs.. and that's what they didn't like. They freezed my accounts.
So, i called SE support center, spent a few $ on the long distance calls. Since i couldn't remember the answer to my security question, they refused to help me.
SE support center is terrible. They wont let you a chance. Since i only had a few days in game, i didn't bother and decided to start a new account, and this time, with a different email.
Now, if you do remember your answer to that security question, they will help you out. Call support center, and/or chat with them. Try email, also.
If you do not remember your answer to that security question, don't spend on long distance calls, it wont work. Don't even waste your time. I don't know how much days in game you got, but there are only 2 things you can do at this point : find that answer somehow, or start a new account. Sadly, i assure you, there is simply not another solution.
Good luck friend.
Don't ask what your linkshell can do for you, but what you can do for your linkshell ...