Thanks for posting in the Apple Support Communities benas96,
You can limit background app activity with the following steps:
To improve battery life, you can turn off the feature that allows apps to refresh in the background. Go to Settings > General > Background App Refresh and select Wi-Fi, Wi-Fi & Cellular Data, or Off to turn off Background App Refresh entirely.
Maximizing Battery Life and Lifespan
If you need further assistance, providing additional information can increase the chances you'll get a relevant and helpful response from the community.
How long ago was background activity for the app disabled? Do you see background activity for the app in question over the last 24 hours?
Cheres!