Hi @AshwiniS_639795 . The majority of the smarty plans are 'use it or lose it' style. You start afresh each month with a new plan and the old unused data does NOT roll over.
If you look at the Price Guide - https://cdn.smarty.co.uk/files/SMARTY-Price-Guide.pdf - on p5 there are Data discount plans (I think that this is what you were referring to) and they do give back money for unused data.
If you use around 10Gb of data, then the Data discount plans are not for you. I would suggest that you are better off buying something nearest to your needs. The 12Gb plan would currently save you £2 per month and don't forget that you can change the following month if it is not suitable.
Hope this helps to clear it up.
