"Spoken and Unspoken" doesn't complete after killing Cyvion

Hello, can someone be so kind to help me please?
The quest “Spoken and Unspoken” doesn’t want to end.
I killed “Cyvion the Echo Night” few times and yet I don’t understand what Im supposed to do.

We felled Cyvion, the corrupted Cerim champion. But he and his Echo Knights still stalk these chambers, neither living nor dead. We must continue to hone our skills in these endless gauntlets, as our ancestors did.

there have been multiple posts about this, and afaik it is just they way the quest is right now. as there is not more content the whole questline is not finished yet.

Thank you for your reply, you are very kind!