Pop-up "WhatsApp expires today!" - what to do?

If the message "Warning: WhatsApp is expiring today!" Appears on your cell phone, it is a subscription trap. We show what you can do about it.

Subscription trap: "WhatsApp expires today!"

The message from your expiring WhatsApp subscription is being displayed by a fraudulent website. The covert goal is to take out a paid subscription. Please do not respond to this message and close the website in your browser.
The said warning is reported by the website "WhatsApp.cm", which looks suspiciously like "WhatsApp.com". The missing "o" is often overlooked, so the message is believed to be genuine.
Most users also seem to get to the scammers through fairly reputable websites. In the meantime, however, the website has been taken offline and the corresponding advertising ads have largely been removed.

If you accept the message, you will be asked for your cell phone number. Instead of extending the supposedly expiring WhatsApp subscription, you get some simple background images for WhatsApp.
You will then find the full bill of 20 euros on the next bill from your mobile phone provider. However, the one-off payment should not remain. Once you have completed the subscription, it will continue to run.
If you fell for the fraudsters, this is not exactly an advantage, but it is not too big a broken leg. In the following practical tip, we will show you how to cancel a mobile phone subscription.