Cracked screen, now phone totally unrepairable

I handed my Samsung S6 in At Samsung South Africa Constantia with a cracked screen, fully functioning phone, with nothing wrong other than a slightly cracked screen. I then received an email to inform me that the main board on the phone was now also damaged. Apparently this is not under warranty and I have to pay in R2903.87. They replaced the cracked screen with a new one, but handed me a non-functional phone, and I have lost all my information on the phone. When I decided to not pay the money, they asked me to fill in a form to waiver the warranty on the phone. As I have Insurance on the phone, this could not be done. They then decided to \unrepair\" the phone, took back the new screen, gave me back my phone with its cracked screen, but now a phone fully unrepairable. I am convinced the crack was not responsible for the damage to the main board, I took photographs of this if needed, and I spoke to a Vodacom Sales Person who is helping me sort out the insurance, who told me that its impossible for that little crack to damage the main board. Due to the nature of my job I need a phone asap! And I also want to know who will be covering the costs of the insurance excess?"