Additional premium for loaner vehicle

I have car insurance with First for Women, I have been their customer since 2016. My vehicle is at the service provider for repairs. The dealer gave me a loaner vehicle and I got the shock of my life when i called the call centre and I was advised that in order for me to insure the loaner vehicle, I will be charged an additional premium. This does not make any sense at all as this is a replacement vehicle. I am certainly not happy with their service.