-The amount of $1500 on the bill includes the total amount for this month’s bill and the adjusted payment difference over the past 6 months.
The $1500 on the bill includes the total amount for this month’s bill and the adjustment payment difference for the past 6 months.
-The amount of $1500 on the bill includes the total amount for this month’s bill and the difference in charges over the past 6 months after adjustment.
While the grammar is fine, I don’t think your customers would understand exactly what you mean by the adjustment phrases unless this is defined someplace else.
You might consider something like this:
The amount of $1500 on the bill includes the total amount for this month’s bill plus an adjustment based on the difference between your payments and the billed amounts over the past 6 months.