I sent my letter off last week recorded delivery - I await the reply with interest

It seems odd that some people have recieved a text (myself being one of them) that Vodafone thinks you are allowed to cancel with, but others haven't recieved this specific text yet and are annoyed that they can't cancel.

What is this text based on? Data usage? Why have some recieved the text and some not? There must be something that Vodafone are using to choose who they send the certain text to that you can cancel with...