Vodafone Excessive Data Charges

Has anyone else had problems with Vodafone and being charged extra for going over their Data Allowance?

I have been told that during the month of October our 2nd iPhone has used 7.5gb over its 1.5gb allowance! Where as on my own phone, which I am on constantly and receive the same emails as the other iPhone I use 3gb!

I’m very angry about it but would like to know if anyone else has had any experiences of it?