Unable to lodge third party claim

My husband was rear-ended by one of your clients on 30 April. It was a three car pileup, your client was in the middle, my husband at the front and someone at the back. We tried to claim through the insurance of the person at the back as it was his fault, he went into your client, who went into my husband, but they said we have to claim through the vehicle that directly hit my husband. Your client has informed you of the accident but his claim is apparently "incomplete". I phoned in to try and lodge a claim for my husband and the lady I spoke to said that your client needs to phone you to complete his claim in order for us to claim, otherwise we cannot do so. How is this fair? Your client is not willing to phone in and complete his claim, his damage is minimal and why would he want to help lodge a claim against him? I have the ID number of your client, the admission of the man at the back that he started the pile up, the admission of your client of being the middle vehicle, photos of the damages to all three vehicles, I have all the evidence that shows that this accident occurred but you're telling me we can't claim? Please find a way to sort this out.