Thanks for your patience. You will be too late to rely on your consumer rights by arguing that the fridge is not fit for purpose or of satisfactory quality. That is because there is a 6 year time limit to bring in any claim for breach of your statutory rights. So whilst there is nothing stopping you from raising these rights in negotiations, if they refuse to accept this, you cannot take the matter further.
You will nevertheless still have contractual rights under the insurance that you have. Your rights will be solely against the insurance provider, should they decide not to honour the insurance terms and provide the necessary cover. This would only be the case if you should have been able to make a claim but they are unreasonably refusing this and not adhering to the policy terms.
In your case the issue is whether this is a cosmetic damage or not. In some respects it would be because it does not affect the operation of the unit, it is mot the compressor, door hinges, etc so the unit is still usable and is working fine. It is not a safety issue in a sense that there is no leak of gases, although you are arguing that it poses a safety hazard due to the presence of rust.
So there are valid arguments on both sides. In the end only a court can determine if they have unreasonably refused to provide the necessary cover. Before you go that far I suggest you use their complaints procedure to full completion and then also consider using the free Ombudsman service.
This is your basic legal position. I have more detailed advice for you in terms of the options you have should no resolution be reached using the steps above, which I wish to discuss so please take a second to leave a positive rating for the service so far (by selecting 3, 4 or 5 stars) and I can continue with that and answer any further questions you may have. Don’t worry, there is no extra cost and leaving a rating will not close the question and we can continue this discussion. Thank you