Absolutely unbelievable

I've been a Santam customer for well over a decade. I pay almost R2500 each month, have NEVER missed a payment and have hardly claimed during my years with them. I pay an excess waiver of almost R400 per month in order to not have to pay excess if something happens to my Mercedes. It did. Part of my claim is a back window to the car. Initially I was told that I would not pay excess if through the people they assign. Great! Now that it comes time to replace the window, I am told there is a R500 excess because \they can't source the correct window and need to get it through the agents". My problem? If through an agent"