1st, Welcome to LQ.
Sorry, no one else has tried to help you for so long.
I don't really know the solution, but I think I can guide you in re-working your post to fix its problems.
Please try to implement my suggestions by using the "Edit" button -- it's good practice.
- Learn to use the "Code:" block feature for file contents & CLI output. You have at least 3 items in your post that should be in "Code:" blocks, please fix these. One of the reasons for using them is embodied in my phrase "at least 3" -- w/o them your post is so unclear I can't easily tell how many you need.
- Fill in your profile & keep it up to date.
- Which of the many DDNS services are you using?
- How did you test it?
- How do you know "The dns and dhcp service is ok."? -- How did you test that.
- Does "the named user" mean "the user, named"? Remember, in English "named" is a perfectly good word that actually makes sense in your original sentence. In fact, I didn't think of what I now believe you really meant until approx. my 5th reading of your post.
- Commas have spaces after but not before. Not a big deal, but your text is a bit jarring to the eye.
Hope someone will see this & your repaired post, & give you some help.