In order to be able to tell you what's wrong, I need to take a look at your configuration. Keep in mind there is one mandatory precondition for DDNS to work - you must have a Static or Dynamic Public IP address. Dynamic DNS will not work with a Shared Public IP. Assuming you know this rule, the rest should be very simple. My personal favorite is dynu.com regarding the configuration. I suggest you to follow the steps here from the scratch.
Please let me know if you get stuck somewhere, I'd be happy to assist