The problem you face is because you have such a large power increase from standard (i know cars run higher bhp but form an insuracne point of view) the insurance company then ask well what is he doing to warnt this increase and you are regarded as a higher risk as some lower end mods which give smaller increases can be regarded as helping fule economy like a super chip or something

Unfortunatly i think you are a bit stuck and it is always in future worth checking for quotes before you change your vehicle incase something like this arrises

the way i look at it is you have two main options one to be honest if you were to have an accident unless you have something really odvious on the car they will never know the bhp of the thing if you were to have an accident so just dont tell them its that high

the other option is if you can afford to replace your car your self go third party fire and theft as there are plenty of companies out there who will assist you on a no win no fee basis for vehicle damage if you are not at fault and if you are your still covered for what ever you have hit you would just need to stump the money up for your own car but to be honest the drop from comp to third party at your age will be bugger all

the final option is just be a pest to your insurance company
claim to have been miss sold at the time of inception ask them to look into stuff for you and if they promise to do some thing get a date they will do it by as if they respond over 5 working days late they are in creach of fsa requlations and then you can say you will call the fos etc

sorry none of these are the greatest of options the only other thing i can say is if you have a second car change the secound vehicle onto the policy and save some money then look for new insurance or try and transfer onto the other vehicle insurance

As you can guess i work in insurance with a well known but to be honest now very well liked insurance compan if you have any questions or querrys ill be happy to elp just drop me a mail