fallout 3 problem

so my problem is that in the underworld aka ghoul city i killed greta to get charons contract but when i went to go tell him that he is now my slave he sits in a corner and does nothing
i have tried doing it again and agian but it never works  

You talked to the bartender again?  He has an actual contract he gives you.  If that still doesn't work, try stealing the physical contract.

Revert back to another save and try over, or just don't do it.