Hi @johnoooo
The first question to ask is if you are PAYG or pay monthly?
If you are pay monthly, unless you took out the contract before July last year where the monthly allowance would be automatically capped, you would be able to add a data cap to your account through your online account and My Vodafone application.
There is nothing more annoying than being charged extra when it can be avoided. There is further information here: Monitoring your data usage
To turn off mobile data, this can be done from the phone settings and by by pull down at the top of the phone. You can also go into the phone data application and set the monthly limit, this stop you going over the monthly allowance. If you refer to the device guides link below you will be able to see exactly how to turn off mobile data and set the data limit through the phone application Vodafone device guides - Samsung S4 mini
edited to add: I have looked through your previous threads and notice you are PAYG. I have moved your thread to the correct board.
