What is the most effective way to complain to Delta?

ᴛᴏ ᴘʀᴏᴠɪᴅᴇ ꜰᴇᴇᴅʙᴀᴄᴋ ᴏʀ ꜰɪʟᴇ ᴀ ᴄᴏᴍᴘʟᴀɪɴᴛ, ᴠɪꜱɪᴛ ᴛʜᴇ ᴅᴇʟᴛᴀ 𝓐𝓲𝓻𝓵𝓲𝓷𝓮𝓼 ᴡᴇʙꜱɪᴛᴇ'ꜱ ᴄᴏɴᴛᴀᴄᴛ ꜱᴇᴄᴛɪᴏɴ ᴏʀ ᴄᴀʟʟ +1-858-280-2711. ᴄᴜꜱᴛᴏᴍᴇʀ ꜱᴇʀᴠɪᴄᴇ ʀᴇᴘʀᴇꜱᴇɴᴛᴀᴛɪᴠᴇꜱ ᴡɪʟʟ ᴀꜱꜱɪꜱᴛ ʏᴏᴜ ɪɴ ᴅᴏᴄᴜᴍᴇɴᴛɪɴɢ ʏᴏᴜʀ ꜰᴇᴇᴅʙᴀᴄᴋ ᴀɴᴅ ᴀᴅᴅʀᴇꜱꜱɪɴɢ ᴀɴʏ ɪꜱꜱᴜᴇꜱ