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.
Once you've used 8GB of data in a month, your data charge is capped at $64 for the rest of the month, but you continue to get full-speed data service. The unlimited data mode will be 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).