Can't progress with the Business Rivals Quest (Bug?)

So I talked to Grog at the bridge, got the quest to kill Marg, payed Grog (for the EXP), went to Marg, got the quest to kill Grog and killed Marg. Now I'm trying to tell Grog that I killed Marg (so I can get the EXP) and then want to kill Grog. But Grog only says "What are you waiting for ..." and then I only have the end-conversation option, so I can't finish the quest to get the EXP (and I really need that to level up).
I searched the internet, but I can't find anything about that issue. I tried saving and reloading, teleporting somewhere else and coming back, spirit vision (Marg doesn't leave a spirit behind), but nothing worked.

Also, I'm in an honor-run, so going back to a previous save is not an option. Do I have any chance to fix this or do I just need to accept that I'm not going to get the EXP and just kill Grog?