If you inform VM that you do not accept the changes in the Terms and Conditions. they either have to keep you on the old terms before the changes, or cancel your contract with themselves by giving you 30 days notice.
Once they have been informed by yourself that you do not accept the changes they have made. they can't hold you to them. they have to do one of the above. they can't automatically sign you up to the new terms if they are not acceptable to you.
If you want to cancel your contract that you are still tied to with them, then you can do it the easy way and contact them telling them that you do not accept the new terms and you want out.
They have to let you go, they can't hold you to the rest of the term of the contract and they cannot penalise you either for ending the contract early.
It has to be said that you only have a certain amount of time to inform them of not accepting the changes, this is usually around 30 days after the new terms have been published. that is one reason why they do not make any effort to let you know of any changes they have made.
Also note that if they persuade you to stay with them by means of a special offer, then these usually mean you entering a fresh 12 months contract, and also means that you accept all changes to the T&Cs.
note to admin - this is about changes to the T&Cs in general. not just to do with Phorm 