I spoke to o2 on the phone and they couldn't locate my order, they needed an order number starting MS-... so I called Virgin on their sales number and followed the option tree to get through to someone (waited about 20 minutes at 18:00) and the person I spoke to was actually great and managed to locate my order. I'm not sure what went wrong but the sim card hadn't been issued but after the call the email came through immediately and now apparently the sim card is on it's way in the post.
I would get all your information like: order reference number, any temporary phone numbers they provided for you or your last bill amount and then speak to them on the phone. They were both really helpful! I called 0344 809 0202 for o2 and 0345 454 1111 for virgin. it took over 30 minutes for each call but was worth the time.