Unable to add mobile number to apple id

I've signed up with a telco and gotten the number +65 8099 XXXX. Unable to add mobile number to apple id. Error msg prompted was invalid number, but number is valid. Reached out to telco but was directed back to apple.

Telco advised that my new number 8099 is a new account segment and Apple has not yet included this in the verification.

Anyone has the same issue or knows how to solve this?