Re: Cancelling mobile phone contracts early....?
Some observations - the contract conditions you sign up to will usually prevail for the duration of your minimum contract term, any subsequent changes being automatically applied on the 13th or 18th month (as appropriate). If the changes are to be applied immediately, then you will have an opportubity to decline them, but you have to do something positive to opt out, you cannot simply cease using the service and expect that to suffice. Sorry.
Being sent a 'text message' of changes to the contract is immaterial because there is no guarantee that the phone user is actually the contract holder, so material changes must be served in writing, not as a text (although both is acceptable).