I will review everything but upon quickly reviewing your reply there is one HUGE issue.   

Creating a bill is incorrect - that's creating a duplicate invoice for the same items and wrongly increases my cost-of-good sold.  

Scenario - I ordered materials for products I sell - that invoice goes to the category "cost of goods sold".  I paid that invoice in full with my credit card.   The materials were defective - so I returned them.  My vendor balance is zero.  

I need to create a credit (credit due to my credit card account not my checking account) which shows the product was returned to that vendor.  That credit must also reduce my cost-of-goods sold for proper accounting.  

When the vendor issues that credit and it downloads to my credit card account, I need to match it to the credit on that vendor.  

In the end the vendor should show a zero balance AND zero past due.  Everything I tried either shows a negative balance, a past due amount or both.  

From what I tried on this post