Mr. Amol Shete,
Before we discuss about case laws I would like to bring to your notice a very recent notification and circular issued which has clarified that those who are already registered as First Stage Dealer or Second Stage Dealer need not get themselves registered as an 'Importer' and vice versa. Thus the Board has corrected its mistake committed in 2014.
please take a print-out each of Notification no. 30/2016 CE(NT) and circular no. 1032/2016-Cx both dated 28.06.16 and try to convince the authorities that passing on the SAD by an FSD or SSD without getting registered as an Importer is only (at the most) a procedural lapse and credit can not be denied on that ground. The fact that once a person is registered with the department as a Dealer he is eligible to pass on any duty under the cover of a valid invoice & he need not get registered separately as an Importer is proved by the issuance of new notification and circular mentioned above.
If following factors are in your favour then there are various case laws which held that substantial benefit or credit can not be denied on the grounds of procedural lapse.
1) Is it a valid invoice/are they valid invoices issued under Rule 11?
2) Does or Do these invoices contain the required details specified in the rules?
3) Is the receipt of material and its use in the production without/beyond doubt or not challenged ?
4) are the dealers registered as FSD or SSD ?
Then put your foot down, convince your management and let the department issue SCN, Then you can contest it.