I am having a similar problem. First it worked but today it doesn't. I have contacted Vodafone and they are sorting it out. I will let you know how I get on.
Edit: OK, Vodafone told me to check that my Mobile Network was set to Vodafone (it was) then to change it to any other than Vodafone, and then after a while change it back to Vodafone! They said it won't work immediately and to give it some time.
So, I am giving it some time