I suppose the answer would be…
If you didn’t use up all your data, you bought too much. Buy less next time.
If you use up all your data early.. buy some more, and plan your future usage.
Maybe I’m a bit strange in that when I have data left over, (every month) it doesnt bother me. I have ‘unlimited minutes and texts’ but I’m not calling and texting 24 hours a day 7 days a week for a while month.
What really gets my goat is my monthly purchase only lasts for four weeks in February, and sometimes one more day. But normally there’s three days difference..😂