There is a usage record in my usage record history. But I have not used Internet during the said period as appeared in the usage record history

System will update data usage records in 300MB blocks. If your previous usage session is less than 300MB, current session will not appear until the system receives data to fill 300MB block. Once this 300MB block is complete, it will appear in the usage record history. During this process when updating the entry, the system will use the time and the date where 300MB block is completed in full. However, sessions with less than 300MB can appear in the usage record history if the customer happens to restart - the router intentionally or unintentionally (power failure/router switched-off)