Regulated entities and government communications from 1600 numbers cannot be blocked by any application. Promotional calls from the 140 series can be blocked using the DND registry. Trai mandates 1600 numbers for trustworthy service and transaction calls to existing customers. Registered telemarketers use the 140 number series for promotional communications. Customers can register preferences on the DND registry to allow or block these promotional calls.

Source: Can't block calls from 1600 no. series, but can put 140 series on DND: Trai