You could cancel them has they are in breach of contract
exactly,
you have bought goods not fit for purpose
I'd ring the local trading standards to get some advice but would think you are legally within your rights to break your contract and go elsewhere.
It turns out that it's the Citizens Advice Bureau who deal with this type of thing and not Trading Standards.
Apparently, in every mobile phone contract there's a clause which states that the phone company only endevour to provide a continuous network coverage and will take reasonable steps to rectify network faults and failures.
Breach of contract only applies if Vodafone singles me out for no real reason. i.e. If they stop me from using the network while it is working and I've paid for the service.
So, thanks to Vodafone, I've wasted an entire morning when I could have been working and I've made 16 landline calls all of which I'm paying for.
Vodafone could give me no information about when the fault will be fixed, what the actual fault is and if anyone is working to fix it at this point in time. Customer service at it's very best - they don't even bother to really respond to complaints on their website forum.
http://forum.vodafone.co.uk/t5/Network/BN1-Brighton/td-p/1506696/page/2