So I was playing the dragonborn dlc and I finished it ( killed miraak) and I thought it was all over but his little cult is still sending members to kill me? Is this normal?
It sounds like a bug. According to UESP, the random cultist attacks are supposed to stop once you complete the quest At the Summit of Apocrypha. I'm not sure about the cultists who stand around near the All-Maker Stones, but I think they're supposed to disappear too.
You could check your quest journal to make sure that that quest is marked as complete, but it probably is, if Miraak is dead. If that quest is marked as completed, nothing comes to mind for trying to stop the cultist attacks.
If you're playing on Windows, you could use this console command to check your quest stage:
It should say
GetStage >> 1000.00. If it doesn't, you can try this to complete the quest:
SetStage DLC2MQ06 1000