In compliance with the directive from the Nigerian Communications Commission, telecommunication companies have initiated the process of replacing old Unstructured Supplementary Service Data (USSD) shortcodes with new harmonized ones.
As a result, well-known USSD codes like *556# have become outdated. Customers of MTN Nigeria have reported to The PUNCH that when they dial old USSD prompts, they are now redirected to a message stating, "Y'ello Our codes have changed."
read more ;https://punchng.com/telcos-phase-out-old-ussd-codes/
source; punch