Conversion from tenancy to ownership

Tenants in a 65-year-old Kolkata building are facing a significant discrepancy between their agreed conversion price to ownership (approx. Rs. 1000/sq ft) and the official circle rate (approx. Rs. 4500/sq ft). Despite approaching the IGR, they've received no resolution. A CA has advised that paying registry based on the higher circle rate and the landlord based on the lower agreed rate could lead to IT notices. They are seeking guidance on how to proceed.