Assign and form system - making changes

I have a system made by someone. But this person left the work undone and doesn't answering, also there was a lot of problems during the work. It should be done quick but took a month!!!! And I have now a lot of problems because of this delay. That's why I will not pay not even a penny before all is done. I've trust once, but not any more. The assignment system is almost done, I take care about some changes, but I need some corrections to be done such us changing the dropdown menu list into a table, adding names of user below the status and making a bulk upload of information to the mysql. The forms are also almost done, but I need to make changes, to make the registration forms as dropdown menus, also to changing the fees, making an approve list of users, changing the printed form, and some small corrections. Because I know that last time it was hard with communication with the creator I will give a 10 days time for all of that. And because I've paid already the whole money for the project, that is undone I will give for the changes not more than $100. And please, don't ask me for some money before the work. I want give not even a penny.