I have around 36 hours left until the current period of my mobile data plan expires. Each period takes 28 days and I have 2 GB of mobile data and endless calls and text messages available, for which I pay 7,99€. With the start of the next period I have 3 GB each 28 days.
In the current period I still have 1,8 GB left, so I only used about 10%. That's mainly due to me staying a lot at home, where I have unlimited WiFi with my phone or a wired connection with my computer. But in months where I visit my family, I usually use around 500 MB, sometimes around 1 GB. Only when I'm away from home for a week or too and have no WiFi options, I will probably come closer to the limit.
Especially for someone who spends so much time on the internet, it's strange that I only use so few mobile data. I don't like to watch videos on my phone on the go. I listen to music on the go though, but often that are songs, which Spotify has already downloaded or cached. Now that I don't use Instagram on my phone anymore, that's another reason for my low mobile data usage.
What I do more extensively on the go, is reading posts from the fediverse via my microblog, reading articles using Miniflux (and the Firefox Preview browser - with tracking protection) or messaging via Telegram. But although I consume a lot of content this way, it seems that using services that don't track you a lot, helps a lot with reducing mobile data usage.
Unfortunately it's already the smallest plan and although I don't use much mobile data, I still need it. It's a prepaid option, so I can cancel each month and am more flexible. When my provider decides to offer a new plan with less data and a cheaper price, that may be an option for me.