MacBook Air INTERNAL PHYSICAL DAMAGE WITHOUT ANY EXTERNAL PHYSICAL DAMAGE

I bought an Apple MacBook Air on the 15th January 2021 for R18,890.00. The product was taken home and being used by my daughter for her online University schooling. Some lines developed along the right hand side and bottom edge of the screen on the 20th January 2021. I immediately took it back to the Shop and they insisted that they send it to their supplier. They did an initial inspection in the Digital Experience shop and found it scratch-free and noted it on the Repair form. I received a phone call today (2nd February 2021) to say that the MacBook was found to have an internal crack on the screen due to physical damage(negligence)and that I should now pay an extra R8,362.94. This report was made by their supplier, CORE GROUP. I questioned the issue of negligence without any sign of physical damage on the outside, but I have been told that there is nothing that can be done except that I pay for the repair. I asked for a refund or Product replacement but they have completely refused since I returned it within the seven(7) day return policy.