Vodafone have extremely weak systems, it's recommended that you always check your bill and query it as you are quite likely being overcharged. They randomly warn you if you are exceeding data limits, only sometimes offering you the opportunity to buy new data packages. If you don't get these warnings then the responsibility is on you to monitor your usage, and if you don't, you will get a very nasty surprise. Their excess data charges are criminal.

The only good thing is their roaming (data and calls), other than that it's hard to see how they can claim to be a leader in service availability and performance, their 4G is less available than others and does seem to operate considerably slower than other providers I've used in UK and abroad.

Recommend you look at alternative providers.