I did a quotation, with the exact same details firstly with the 3 points, and now without ... the difference over 12 months was only £300, not £1000

Hello, I recently attempted to renew my insurance policy with my existing company. When asked about any convictions, I thought I was reminding them that I still had the 3 I already told them about 11 months prior. When looking at my policy for this year I notice it was not on there... She then came back to me after around 20 mins, and told me that because I hadnt been paying the correct premium for 11 months, that they are going to backdate my policy premium by £1250 !! That is their judgement of 11 months with 3 points, I feel sick and dont know where to turn, I paniced and ended the phone call after trying to plead a case. Can anyone help or advise? I understand that you have to pay for back dated errors or what ever else, but SURELY this amount is unfair? Its like theyve told me straight, £1250, they could of got that figure from anywhere.