Poor Insurance

I got a quote from them for my new car. I accepted the quote and when I received my policy there were 2 cars on it. I immediately send them a mail to query. I downloaded the app and only my one car was on there with my premium as per my quote. When they removed the second car my premium increased. According to them I now removed the second car which I never added to it. How can it be my fault if I only insured 1 car and they made a mistake on their side? They have removed the second car but are now refusing to adjust the premium as per my quote received and as per the app?