I thought I had a low usage with my 1.5 years' worth saved. Only reason I paysfor that plan is anything lower and my provider does not offer rollover.
Eg here in slovenia, if you want unlimited calls and texting, you get 150GB in your "package" for 9.99eur, but you somehow can't save that data for the next month.
https://www.hot.si/ponudba/paketi.html (not affiliated)