Just get the rego and company. From there you can ring them and explain the time and place it happened which is fairly easy to check out for most now as we use satellite tracking. I have worked for 3 truck companies and am responsible for satellite tracking etc as part of my job.
I now work for the parent company of a very well known aussie icon in trucking and we get legitimate and bogus claims most weeks. I assist in checking them out and we always pay up if the claim is genuine.
I also hear of claims from dumbass's who mistake our company name for that of a well known hire company so we get their calls too!!
Also remember, most won't know it happens and heaps of people flash at trucks for going slow, changing into their lane etc.
Unless they are tipper trucks, most companies will have some kind of tracking as it is generally a KPI put in place by the customer.