[help] I can't complete the bloodline quest in the Dawnguard DLC

I am not sure if I have missed something or done something wrong, but after I refuse to become a vampire from lord Harkon and get banished from his castle I get no indication of a complete quest or where to go next. I have returned to fort dawnguard and spoken to Isran however he still has the same dialogue options that he had after i recieved the quest, I have searched online but the only things I found were related to getting into the castle in the first place.

There is a bug report on the wikia saying

"If the player chooses not to accept Harkon's gift, there is no indication that the quest Bloodline has been completed, which creates confusion when A New Order is completed."

but there is no fix for it.

any help is greatly appreciated.