You must ignore the DRA letters. They are powerless. Never, ever, communicate with a useless DRA. They can't do anything and are not a party to any contract allegedly breached by the driver. Ignore.
At some point, after the DRAs have given up, you will probably receive a Letter of Claim (LoC), come back if/when you receive one of these. Besides telling you it is an LoC, it must also give you 30 days to pay, not the usual 14 that DRAs give.