This is most probably due to pro rata charging after your upgrade and you have got more than one months billing, which could be around 7 days line rental to your billing date.
When you upgrade, your account will be reset and your first bill will be on a pro rata basis and your will receive a proportion of the months allowance as with the charges to your billing date. As line rental is always charged in advance, Vodafone will have also added one months line rental to to your first bill after upgrading with the pro rata charge making your first bill one month and part of a month.
Your online account will give you the dates for the pro rata period and the extra months line rental and you should also see the line rental credit.
You will probably find your next months charges will be for the agreed monthly charge which you agreed with Vodafone when your upgraded but if these are incorrect, or if you have any further enquiries, the forum or Customer Services will be able to help.
You should receive an email confirmation within the first week after upgrading detailing all that was agreed with Vodafone when you upgraded.
