They probably tested more for local issues than upstream. We are frequently seeing the problems in play around the exchange points into who the ISP assigns for the peering/transit to Ormuco in Montreal.

Need to get a more proper analysis of the specific connection to the servers...at least a tracert so someone has a roadmap to follow. Blizzard has a nice how-to for testing to their servers. Can apply the same guide, only using the addresses for this game. Here are the registered names for the lobby servers in Canada:

neolobby02.ffxiv.com
neolobby04.ffxiv.com
neolobby06.ffxiv.com
(for the Japan lobby servers, use numbers 01, 03, and 05 in the names)

The guide details how to create a log file of the trace in the root of your C:\ drive. You should save a copy of it to another location, and then run another report to some other services--like maybe a Blizzard server or the server for another on-line game that plays well, and perhaps another for another service that may be behaving well (youtube, netflix, hulu, etc.--even google would help). Make these reports available to your ISP for review--be that a copy/paste into an email or forum post, or direct attachment.

The goal is to help narrow down where the problem is occurring. They may show things consistently bad at one particular gateway on their network--or it may be fine all the way out to the perimeter of their network, but then it goes sour at one particular exchange point...like the one you use to get to Ormuco in Montreal specifically for this game. Then they know where they need to look---and it likely is not something in your neighborhood.