late payment

Hello Sharron
So there is no dispute on the last invoice. He is just withholding payment of the invoice because because of a dispute with another company.
I think you should make it clear that the products supplied by the other company are nothing to do with you and that he cannot use that as an excuse not to pay you!
Depending on the amounts involved it may be beneficial to try and resolve the situation with the other company and the missing parts. That will be an easier solution in the first instance.
If you feel though that he may be making excuses to deliberately avoid paying the invoice (even though he paid the other two) then you may need to consider a different approach.

I hope that helps

David