Lost Parcels refuse to pay out claim

We had 3 parcels due to us from a customer.
As most are aware they run a barcode scanning system. The stock was collected and not scanned. I then get an email for Interlink to say this had been delayed.
2 days later I receive 1 of the 3 parcels. This had a completely blank Interlink Parcel Label, clearly reprinted. The consignment no relation to the 3 parcel consignment number.
The contents were correct, so was clearly 1 of the 3.
After over a month of constant phone calls, contradicted information from DPD and very poor customer service I finally received the claims form.
The claim was rejected on the basis the driver had "left" the company. And they had no evidence 3 parcels were collected only 1.
No reasons as to why the parcels were missing or relabelled. They have not logically looked into the evidence, and I am now at a £650 loss.

My questions are:

Why would only 1 parcel be collected?
Why was only 1 parcel relabelled?
Why did the driver not confirm on collection 1 parcel was collected out of 3?
Why did the driver not scan 1 parcel in?
Why do we have several confirmations 3 were collected in email and on the phone the silver team How can you base a case on a system which is obviously flawed from the scannin system itself?

As a regular user I have advised all my customers and staff to avoid DPD until the matter is corrected.