Disappearing data

In reply to an sms sent to me from Vodacom (Judy Chetty) but one does not have an opportunity to reply on that platform. I have a book in which I record my data usage. Every time I log onto the internet I record the date, day time date, my night owl data and the total volume. The same goes for when I log off the internet all the data used is recorded again. So I do not just thumb suck my data usage. I also know when my unused data is supposed to be carried over. So I do know when my data disappears.