don't use the word front splitter, as that is a performance mod if its an actual wind tunnel tested motorsports item, what you have is a front lip, or front bumper body styling addition. that should put you back on the insurance list. although it sounds like you found a new insurer.
best bet is to use the likes of sky insurance, or Chris knotts or Adrian flux etc, they are set up to deal with performance and modded cars and offer; in general a better and more comprehensive service, and you get to speak to a knowledgeable human being.