I've just been contacted by Vodafone via the phone. They say that they cannot cancel my contract yet, until I can prove that the new charges directly affect me, even though all they have to do is look at my previous usage. Every month since I started my contract, i've been way over the 500mb limit. Apparently all I have to do is wait for my next bill to come through, with the extra charges, then call them, and they will "review my contract". Success!
Given you are already reaching your allowance and in some cases are over, from June 1st, you will start to receive an alert to say you've gone over your allowance. We will be tracking your usage, and in the following months if your usage continues to be over your data allowance, we will contact you to discuss alternatives (including for example, upgrading to one of our mobile broadband plans) and that you could incur charges. As you know we have a Fair Usage Policy and for the vast majority of customers, they do not use more than their data allowance. This Fair Usage Policy has always formed part of your price plan Terms and Conditions and due to this we are not in a position to allow you to cancel your contract without penalty