Here is their official response to me over email (2.5 months ago with no reply afterwards):

Dear Customer,

Regarding your request for support. Please find your answer below.

Thank you for contacting the Square Enix Support Center. We apologize about the technical issues you are experiencing, if you are seeing a lot of packet loss over your ISP's network there is not much we can do in regards to that. We suggest contacting the ISP in question and see if they can change the networking route that it takes to connect to the game. If that is not possible we can offer a few things for you to try to circumvent the issue. However, if the issue is being caused by huge packets being lost over your ISP's network to connect to the game servers, there wouldn't be much else we could do. We apologize about the inconvenience.

Thank you for contacting the SQUARE ENIX Support Center.
I've pinged them 4 times in the last 2.5 months without a reply. They really don't care about their player base.