Outsurance not wanting to refund for wrong vehicle insured by them

I had my Gold 5 TDI insured with outsurance in Feb last year. Upon insuring the vehicle they could not pick up my car/model. The agent then advised that because they can't pick it up I have the option of insuring it as a Golf 6 or Golf 4. Thinking that this was a standard practice I agreed. Last month I had the insurance reviewed as the car might be my dad's but I am paying the monthly premiums. They then reduced the amount due to him being a pensioner. Then when speaking to the agent I advised her that my vehicle on the system is not a golf 6 but a golf 5, she then categorically stated that this was not allowed. I advised her to listen to the recording. The agent was then able to pick up the model of my car and the premium rate was adjusted. I then realized that due to the premium rate being higher due to the car being insured for more I now require a refund as I was overpaying. I asked them to go back and initially review what the premium would be before a pensioner's rate and deduct that from the amount that I was paying for the gold 6 instead of the golf 5. They then came back and only calculated monthly interest for 10 months and refunded me. When I requested to have a breakdown since Feb 2021, the amount of premium for gold 6 and premium for gold 5 and then deduct that amount ad refund me accordingly. Up until today have not sent me the breakdown I required. I also requested the CEO's email and still nothing. What if my Dad had been in a car accident and the assessor sees it as a golf 5 and not golf 6, then would they pay out? certainly not and then I would be accused of *****? I would like my refund.