Incorrect purchase invoice due to not executed early payment

In februari this year I orderd several items from my new supplier. The bill was put into the system with no discount or supplier credits, and was payed in full. Two months later I ordered again and I added this bill for the compete amount as a purchase invoice without any discount or early payment.
But instead I have to pay the complete amount, there is a line on the purchase invoice that mentioning that the mount of payment is lower beacause there was allready an earlier payment.
This is incorrect because the first bill was payed in full and the second one still has to be payed in full, and there was no partial payment, of credit.
I think there is a a slight problem in the program. please help!!

Was the original purchase invoice properly completed as being from the supplier?

Also, is there anything in the Suspense account?