https://si.osu.edu/sites/default/files/living_lab/products/delta-airlines-customer-usa-contact-numbers-a-step-by-step-guide-2025.pdf https://si.osu.edu/sites/default/files/living_lab/products/delta-airlines%E2%84%97-customer-usa-contact-numbers-a-step-by-step-guide-2025.pdf https://si.osu.edu/sites/default/files/living_lab/products/delta-airlines-customer-service-usa-contact-numbers-the-complete-2025-support-guide.pdf