You can simply book any data package and then switch the subscriptions back to "off". This ensures that no further data packages are booked after expiration or consumption. 


See: How can I manage, deactivate or pause my subscription in the cockpit?


Here is an Instruction:

Open the customer portal and click on the SIM card in question.

Next, click on "Subscription inactive" and then on "Continue" at the bottom right.


Finally, click on "Confirm".