If you want to continue benefiting from your Wi-Fi Hotspot , you have the opportunity to set up an account with Vodafone [Alternatively, enter network provider of respective country] and purchase the an “Internet in the Car” plan that suits your needs.

Get in your car. Turn on the ignition. Make sure you are not driving.
Connect your device to the in-car Wi-Fi Hotspot, and open an internet browser
Enter a URL in your browser such as http://www.opel.xy (Note: please only use an HTTP-based web address, not an HTTPS one)

You will automatically be redirected to an instructions screen. Just follow the steps.
Set up an account for the “Internet in the Car” portal from Vodafone [Alternatively, enter network provider of respective country]
Purchase a Wi-Fi plan on the portal
Turn off and turn back on the WiFi on connected devices
As soon as you have purchased a data plan, you can continue to enjoy all the benefits of your fast and secure in-car Wi-Fi Hotspot.

After you have set up your account, you can administer and purchase your Wi-Fi plans quickly and comfortably through the Vodafone Internet In the Car portal [ONCE AVAILABLE, LINK TO VODAFONE PORTAL] [ALTERNATIVELY INSERT NAME AND LINK TO LOCAL NETWORK PROVIDER’S PAGE].

Vodafone offers you the data plan which suits your needs best 2 :

Vodafone’s “Daily plan”1 : Best for a single journey. 24 hours or XXGB3 of high speed surfing and streaming for £XX.
Vodafone’s “Monthly plan (28 days)”1 : Ideal for frequent use. 28 days or XXGB3 of data for £XX or XX GB of data 3 for £XX.

1 You can enjoy internet in the car on Vodafone's network when travelling in certain European destinations at no additional charge [INSERT LINK TO ROAMING SECTION ON THE WEBSITE]. Keep complete control: the Vodafone "Internet in the Car" Portal always keeps you informed of how much data you are using.
2 If you do not have an active OnStar account, you may not purchase Wi-Fi plans.
3 The data plan ends either when the indicated time period expires or you reach the data volume as indicated, whatever comes first.