There have been many, many posts on here from customers claiming that they have been offered the 'absolutely best deal we can - take it or leave it'; and then when opting to leave it and cancel, suddenly some days later they get a call from VM offering a deal which is much better than the 'very best deal' previous.
It's a game, it's bluff and counter-bluff. But if you play it, do be prepared for VM to call your bluff and let you leave, and don't call you with a better offer. So be prepared to leave, you have set up with another provider, yes?
Because if you do cancel and then call VM asking to stay; don't be surprised to find that the cost is now higher, and a big red flag on your account, saying 'this customer is a completely BS'er they will threaten to leave, ignore it, offer them NOTHING. They are a MUG who eventually suck up whatever we demand of them....
No I'm paraphrasing, the notes on your account probably don't say exactly that, but you get the idea!