Twice today a 0800 rang claiming to be from vm asking me to give details over the phone so they can Lower my bills. Don't need to ring me. Just Lower them
it will come with another contractual term, so they do need to speak with you.
whether or not it's actually VM calling is something else.. you could verify by contacting VM on 150 / 0345 454 1111 and navigate through the "thinking of leaving" - speak to retentions and ask them if they have tried to contact you / get the reduced price offer.