1. Sir, the important issue is on which date you received Code Number from ESIC (Form C-11) and in the said code number from which date your unit was covered under said Act. If the said date was provisional, the question is whether now the Social Security Office (ESI Inspector) has finalized the date of such provisional coverage after verification of records. If so, from which date? Whether amount of Rs.20 lakh has been assessed on adhoc basis or is on actual basis ?. If on adhoc basis, you can request the said department to assess the contribution on actual basis(if otherwise favourable to your unit) after verifying your records. Everything depend on facts of your case and your decision since we are not in a position to offer any more comments on issues of facts.
2. Sir, whatsoever, the facts may be, if coverage is definite, you have no alternative except to deposit the amounts of contribution. This was clearly mentioned by my seniors/experts S/Sh. J.S.Malik ji & Madhu T.K. ji in their remarks as above. This amount of contribution as mentioned above, I think, may not include the amounts of damages and upto date interest, and I think, the said department will make separate claims under these items.
3. Sir, in my opinion, if you have any legal plea against such coverage, then you can also challenge the same in the Employees' Insurance Court of the area where your unit is located and you can file the case by engaging an advocate. Perhaps the Advocate can also take plea that the amounts of contributions pertain to a period of more than 5 years, for which some limitation has been laid down in Proviso to section 45A of said Act. This also depend on facts of your case and earlier decisions of Hon'ble courts, if any. With best wishes.