Urgent Advice Needed on Unfair Salary Deduction After Resignation

I resigned from my company after receiving an appraisal. At no point during my resignation process was I informed of any policy stating that an employee must stay for six months after appraisal or face a salary deduction. When I first submitted my resignation, HR and my managers did not inform me of this policy. Around 15 days before my last working day, I followed up via email to ask if any pending formalities were required—again, no mention of this policy. I sent another email when only 3–4 days remained in my notice period, specifically asking about any required exit formalities. Still, no one informed me of any recovery amount. Even during my final exit formalities at the office, nothing was communicated. Now, at the time of my full and final settlement, I have been told that an amount will be deducted as per this policy. The company claims this policy was mentioned in my appraisal letter, but they never provided me with this letter, and I have never signed or agreed to such a policy. I believe this is unfair and potentially unlawful, as I was never made aware of or consented to this policy. Can the company legally deduct this amount without my prior knowledge or consent? What legal actions can I take to challenge this deduction? Would appreciate guidance on how to proceed. Thank you.