ATM did not give cash but my account was debited

What usually matters in this situation, and the papers to keep ready before you meet an advocate or free legal aid (call 15100).

Your situation

Transaction reference (UTR / RRN), date, time and amount
The bank tracks failed payments by this reference. Where: UPI app history, ATM slip, card slip, statement.
Debit SMS and the statement entry
Shows the money left your account. Where: SMS, net banking statement.
ATM slip, ATM ID and location, and exact time
The bank checks the ATM's records against your claim. Where: ATM slip; ATM ID is printed on the machine.

Written confirmation from the shop or person that they did not receive it — Strong support where your app shows "success".
Bank complaint reference and all replies — Needed for an RBI complaint.
Raise a written complaint with your bank and keep the reference — Starts the formal process and the record for compensation.
RBI complaint (cms.rbi.org.in) and its number — Available when the bank rejects or does not resolve within 30 days.

Timelines come from RBI's 2019 framework on failed transactions. Your advocate or the bank can confirm the current rule.

General information, not legal advice.