RAC - like any insurance company nowadays they simply cannot be trusted.
RAC insurance cancelled the insurance of one of my colleagues rather then renewed it as requested. He was then stopped a few days later at a police roadside checkpoint on the A5, arrested and charged for no insurance. I had to go and pick him up.
Took him days to get the RAC to check the instructions they received by phone. He was left without transport and no ability to get a hire car. In turn, that cost the company tens of thousands because he wasn't able to do his job as a PM working on a national project with very tight timescales and penalty clauses.
It was eventually put right and the RAC instructed the police and court to cancel charges and any record of the incident on his details as it was entirely their error. He still had to pay the costs to get his car back until the RAC paid him back.
It's getting to the point where you have to record your phone calls with the insurance as they do you and tell them you are doing so. They give you a whole spiel from a script but I think you now have to tell them to point out any significant clauses and omissions that might not be apparent. They place massive emphasis on you being honest with them, but doesn't seem to be true the other way around.
As far as Classic Car status - ask them to show the evidence that they specifically and clearly advised you of this policy status and condition when you took out the policy and where within that notification that NCB (a standard insurance item) was stated as not accrued, and that finally, you asked for and accepted that policy with that condition - especially if they asked for NCB to provide a reduction in premiums. If you made the arrangements by phone, ask for a copy of the recording. I expect they cannot do that.