To be very clear, there appears to be no escape from statutory laws and rules/regulations framed thereunder. However, you may also agree that you may be counting coverage of persons on the basis of the present wage ceiling, but you know that before 01/05/2010, there was a different wage ceiling. So, if coverage is determined since the start, there may be more or fewer coverable employees. In addition, under the said Act, all casual or temporary employees are also coverable, which I think you may have not counted. However, if you desire and like, you can share with me the following information through my email so that I may be able to make you clear about rules/regulations:
1. Whether your establishment is a factory coverable under section 1(3) of the ESI Act, 1948.
2. If not, whether your establishment is a shop or another establishment for which the State Government (appropriate Government) has issued a notification under section 1(5) of the said Act. If so, detail the exact activities in your establishment. As mentioned by you, your establishment is doing the work of Accounts Outsourcing. Hence, in my opinion, it qualifies as a "shop" and is coverable under the said Act.
3. Whether you have a copy of the notification under section 1(5) issued by the State Government if your establishment is among those establishments as notified under section 1(5) of the said Act.
Regards.