I have a O2 contract phone. Dd has a t-mobile pay as you go. Suddenly she can't text me. She can ring me, I can send her texts and ring her, but if she tries to send me a text it looks as if it has gone, but doesn't arrive at my phone. She can text other people, including other O2 contract pphones. We've tired all the obvious - she's using the right number, neither of us has blocked the other - any ideas?