Who will be held responsible for an invoice that was not signed?

We delivered goods to a company through a truck company that has done this in the past as well. The delivery was done in May 2015 and the company refuse to make payment due to never receiving it, the invoice also was not signed that was given to the driver. We have been struggling to get information and payment from the company it was delivered to but at no avail, as they stated they never received it and gave records of the week we delivered it with nothing showing up. Who will be held responsible for this invoice, me (Admin), Truck Company or Client that never received it? The truck company does state they delivered it to the correct address, but there paper also was not signed, we paid the delivery fee and have all the documents for payment.