Additional Stampduty payment notice for flat

I have purchased my flat (resale) and paid stampduty and registration charges on 31.03.2010. Purchased flat higher than market value. Hence Stampduty and registration was paid as per following: Stampduty = 3.69% of purchase value (E stamping was done on my agreement) Registration fee = 1% of purchase value. I have legal receipts of the above. Now, my society has applied for deem conveyance (building is 28 years old) of the society land (which is under builder's name). but during deem conveyance process they appointed CA and CA has checked details with registrar office. They found that, few members including me have paid stampduty less and there was some mismatch/error during stampduty calculation. T hey are planning to send notice to pay additional 1% of purchase value (don't Know how they arrived this value) to us. My queries are, 1. Do I need to pay additional 1% of purchase value as stampduty ? because my agreement is already registered. 2. Legally who should pay this additional 1%? me or society ? 3. Since the conveyance matter is land for the society, can I negotiate with society to use society fund? 4. If we do not agree to pay additional 1% of stampduty, what will be the consequences ? 5. If we do not agree to pay additional 1% of stampduty, will the conveyance deed will occur? Thank you in advance for all the help.