@Maria1968
The only alert Vodafone send is when you are close to the data allowance and that alert is automated and not to be relied upon.
You Son uses the phone and he should have been aware of how long he had spent on the phone and would have easily been able to check the remaining time and unbilled charges by calling 44555 or from the My Vodafone application. If you are the account holder, you could also have monitored his usage through the online account.
Having a contract means having the ability of using the services without the worry of adding credit and this means managing the account the same way as you would a bank account and not getting overdrawn.
