My OH has a problem with his eyes and was sent a very stroppy letter from dvla stating that if he didn't make an appointment with (they named the optician ) then he would not be able to drive. He had to do this within 1 month and the letter stated that the optician would not be able to give the result, it had to go to their medical practitioner for a decision. The tone of the letter was appalling.
He didn't ask for the result, but the optician did tell him that he hadn't missed anything so he would be ok, but he still had to wait for the result.
Hope you get your problems sorted out. If not, shout loudly, make a fuss!
Don't dvla have targets to meet? Since 'we' taxpayers are paying?!!!