Gratuity & Leave encashment calculation

Please share what is the rule for calculation. Is one of it we calculate on Net & one on Gross? Is possible?
My last company deducted my Notice pay without any communication? Is it legal?

Gratuity is Paid on Last Drawn Basic+DA+VDA
Did you serve Notice Period as required under the Terms of appointment mutually agreed & accepted?

Hi All,
I have left my last company serving the notice pay around 45 days out of 90 Days.After that request the company to settle the pay out by deducting the unserved notice pay & convey the amount which deducted as Notice pay.But company not responded the mail up to Nine months.
After that they deducted notice pay on Gross basis & adjust my leave encashment on Gross basis for unserved days. For that I raise point that why notice pay on Gross,why it not on Basic.If they not.intimate me.for Nine months the it is not my Fault.
Many company deduct notice pay on Basic & settle the leave encashment on Gross Basis.
As our Company settle the leaves on Gross .For it no issue but for Notice pay I am not agree with company to deduct it on Gross.As they are not communicate the same to me before leaving the organisation.
Please guide me about the rules & laws for it.