This issue of the phone connection mysteriously being disconnected once you give notice, has been reported a couple of times on here now - we have to conclude it is down to some complete incompetence in VM's system.
However the situation here is clear, you report the loss of telephony service, irrespective of whether or not you have given notice, VM require you to give 30 days notice and to pay them for this time, similarly they are obliged to provide said service during this time. So you report the loss of service and VM have two working days to restore it otherwise they are required to pay you some £9.50 (or so) per day up to either they restore it or your notice period expires.
Either way, you are legally entitled to the compensation. Now realistically VM's broken and incompetent customer services provision won't actually just provide this and you will need to raise a complaint (expect it to be fobbed off), request a deadlock letter (also expect this request to be ignored), and take a complaint to the Ombudsman service, in which you request full restitution of your costs, so £9.50 or so for each and every day you were without an phone service, plus, I'd say £150 extra for the inconvenience, poor complaint handling etc.
