Hi
Unfortunately if you have claimed for your car being broken into, this will have affected your No claims discount. I would always advise paying to have the protected discount when this option is available. You say the form were never returned, which suggests you did not proceed with the claim. If the Insurance company were subject to any fees relating to the write off assessment, these fees may have affected your NCD. Speak to your Insurers.
Also if you have changed your car and this is rated more highly this would have affected the premium. This would be the first time you have noted the difference, as you may have only paid a pro-rata amount for mid-term adjustment.
In the last 5 years or more I have changed Insurer every year, thanks to the comparison sites like this. In that time I have probably saved approx £30-£40 per year. Luckily I have max NCD which helps and live in a low risk area.
The interest you refer to is the charge for paying monthly Instalments. An apr of 32.1% seems excessive. From what I have seen the interest apr's vary, but appear to be on average about 24%. This is due to the credit crisis in part, Insurers are trying to put people off paying monthly and encourage annual payment. Insurers do incur high costs dealing with unpaid instalments due to unsufficient funds etc and customers cancelling cover by stopping Direct Debits. A few years ago when the economy was booming Insurers were offering interest free payments, because the financial environment allowed this to happen. The world has changed.
Best option is to phone your Insurers regarding the claim to get the details. Then phone around or use the comparison sites if you can to get the best deal. Insurance companies can sometimes rely on customers just renewing, particulary if claim made, therefore not offering the best premium.
Good luck
Huckster