No. Any unused data from the current plan does not carry over to the next plan.

For example, you have a 30 GB plan valid for 30 days and purchase an additional 30 GB plan valid for 10 days.

If you use the first 30 GB after 20 days, the additional 30 GB plan will activate automatically and will be valid for the next 10 days.

If you still have 10 GB remaining when the first plan’s 30-day validity period expires, the unused 10 GB will be lost. The additional 30 GB plan will then activate and remain valid for 10 days.

The plans work consecutively—their data allowances and validity periods are not combined.