So I’ve paid 14.99 for premium through iTunes in order to watch the World Cup and I’m upset I had to miss out due to the fact it said my account had expired when I log in even though I just bought it.
i tried again this morning and a message says that my username or password is invalid
If you subscribed via iTunes, then Apple/iTunes manage your subscription, not Optus. You need to contac them.
It's been a while since I've used iTunes myself but I believe there's a "restore subscription" option that normally fixes this type of thing.