SIM activation is normally more or less imediate, although I think the website says it could take up to 24 hours. If there's a delay, it's possible the activation has failed and stuck - it's happened to me.
In this instance, frontline customer services will usually re-try, but that will fail too as the first attempt blocks subsequent ones. Your best bet is to drop the Social Media team a line on Facebook or Twitter. There's a procedure for dealing with this situation and they're familiar with it.
