Reload a previous save fast travel to another location (perhaps Whiterun) and do it again.
OR
Just travel to Windhelm and find the ship's Captain who agreed to take you to Solsteim for 1000 septims. The cultists eventually will catch you up when you return to Solitude again.
> At the start i was attacked by cultists near a giant settlement but then I left their body's thats when I completed the other 2 add ons. <
That was a big mistake...
Have you tried to search the other cultist for a note ? - maybe it will trigger the Dragonborn quest.
You can try to re-install your main game again and your DLC's as well.
(First install the game - update, then all the DLC's.) - (see your DLC's install order under "DOWNLOADABLE CONTENT", and install them again in a different order.)
Can't say it often enough :-
Make manual save games at important points so you can revert without losing too much play.
Only one thing is certain with Skyrim - it WILL bug or glitch on you at some point so prepare for it.
For the few who report they have never had a problem, ok we know so no need to come in here and state it....again.