Citibank sends OTP to both phone and email - are you not registered online with an email address? The email arrives pretty quickly.
Alternative is of course to book online and go via the internet banking logon - I also use this more often than other means as it's not reliant on a code coming from a different channel.
I get the email, problem is in I am abroad so no access to my local number and I can't book online as its a redemption which needs calling in.