You can see the remaining balance of your roaming package at any time in your customer account. 

1. Follow this link to the login page of the customer portal: Customer portal

2. Log in to your account.

3. Click on "manage" for the affected device or SIM card.

4. Navigate to "Roaming".

5. You can now see the remaining credit under "Data usage".

You can also see the roaming data consumption in the Cockpit view: