Can I transfer unused data to the next month?

No. On the 1st day of every month, you are given 1GB of data that is valid till the end of the month. When there is less than 100MB of data remaining, the balance of your line is refilled with 1GB of data automatically. This data is also valid until the end of the same month. With the start of the new month your data balance is reset to 1GB and you are charged the monthly fee of $8(€7.50).