There is quite a lot of control over data usage on mobile phones. My current complaint is that the controls are not unified, but in many different places.

For example, on Android 17, there is Data Saver mode. Your per-app settings can control mobile data usage, in the background, or unlimited. Your WiFi networks can be individually labeled as metered, non-metered, or automatic. In the YouTube app, there are settings for your video quality, and how to adjust that quality based on your connection, if it is mobile data, or metered WiFi. YouTube Music has its own settings, and since it handles podcasts, you can opt out of video entirely.

Furthermore, there is monitoring of data usage. You can set the time period: for example, my mobile data metering resets on the 9th of the month. You can see usage for each app during that time period, split out between mobile and non-mobile data. I can set a warning threshold and a hard limit for mobile data usage.

I only use free LLMs, and not very much. I've only reached a limit once. But I do see that they have indicators or meters for usage. So perhaps check again, look harder, maybe ask your LLM how you can monitor and restrict token usage.