The way mobile providers charge. The likes of Vodafone, any random Telecom, T-Mobile and so forth. It's a huge scam, bordering theft sometimes. Want samples? Here we go:

"Your credit expires in x days. Better recharge now to not lose it!" (Banks should start doing this /s)

"Your credit has expired. Better give us more money within our generous deadline, or else we are forced to delete your number. We love you."

"Your data has expired. We now charge you a horrendous amount every minute, because we are too greedy to warn you in time. For technical reasons we also cannot stop you from using data after your allowance has been used. Fortunately you still have credit, huh?"

"Your data expires today. We don't insult your intelligence by telling you when. Surely you remember when you bought the package, right? It's not hard to count 24 hours. We also do not send any SMS anymore to save the environment."

"Your data has expired. You need data to buy a new bundle. Our app charges data for our convenience."

"Social media data only works for WhatsApp, but not for Signal. But who uses Signal anyways?"

"Use our customer friendly support chat. Conveniently it uses data. 'Hello, I am your smart bot speaking. How can I help you? I might understand you if you type one of the three questions I have been programmed to answer. Do you want to know more about our products?'"

Edit: added point 2, minor corrections for clarity