Here I am providing important phone numbers of Citibank for Global Credit Collections for your reference:

Australia
Toll-free: 1-800-252-856

Bahrain
Post Account Opening Toll-free: 8000-4884

Canada
Toll-free: 1-800-248-4674
Pre Account Opening Toll-free: 1-866-703-2462

UAE
Pre Account Opening Toll-free: 8000-172-122
Post Account Opening Toll-free: 800-035703463

Hong Kong
Toll-free: 800-908-413

India
+91 22 4955 2484

Singapore
Toll-free: 1-800-225-7211
Post Account Opening: 65 62257211
Pre-Account Opening: 800 101 2342

Thailand
Toll-free: 001-800-65-6196

Europe
Toll-free from UK: 0800 032 2484
Toll-free from Europe: 00-800-2484 2484
Pre Account Opening Toll-free: 0808 101 7384

USA
Toll-free: 1-800-248-4674
Pre Account Opening Toll-free: 1866 703 2462
Email nrinfo@citi.com for pre-account opening queries

Mailing Addresses
Bahrain
Citibank NRI Business, Citibank House, Al Seef District, PO Box 548, Kingdom of Bahrain.

Dubai
Citibank NRI Service, Al Wasl Building, 7th Floor, Oud Metha, PO Box 749, Dubai, UAE.

India
Regular Mail:
Citibank,N.A., PO Box 4830, Anna Road Post Office, Chennai 600 002, Tamil Nadu, India.

Registered or Certified Mail:
Citibank,N.A., Mail Room, #2, Club House Road, Chennai 600 002, Tamil Nadu, India.

Singapore
Citibank Singapore Ltd., NRI Business Center, 8 Marina View, Asia Square Tower 1, #21-00, Singapore 018960.

USA
Citibank NRI, PO Box 431, New York, NY 10013. Please do not send USD (or any foreign currency) cheques or cash to this PO Box address.