Check your HDFC Bank passbook
Check your HDFC Bank account statement
Check your welcome kit or account opening documents
Check your net banking profile details
Check your mobile banking app profile or account details
Check your cheque book if customer ID is printed there
Call HDFC Bank customer care and verify your identity
Visit the nearest HDFC Bank branch with valid ID proof
Check emails or SMS from HDFC Bank sent at account opening
Use the HDFC Bank customer ID retrieval option on net banking or mobile banking if available