If everyone that's with Sky could contact their customer support either via phone or email hopefully it'll help them actually acknowledge the problem and get it fixed. I did a quick Live Chat session with a Sky representative and they didn't really take on board what I was saying; just told me to contact Squre-Enix.

I've sent a more detailed email to them now, however. Hopefully if they get multiple support requests / complaints they'll actually have to do something about it.

(Also worth noting I emailed Square-Enix, too. They told me to try Port Forwarding (which had no effect) and then to contact Sky.)