Failure to meet warranty obligation

I have a Sony Xperia Z3 compact on contract which I've had less than a year and the screen started lifting away from the phone due to a design / factory fault. It's well documented that the heat from the phone melts the adhesive which causes this. I've just been told that I will need to pay R2800 to get it fixed as the phone is out of warranty due to me damaging the phone. When asked what damage I caused, I was told the screen is lifting. I asked to speak to a manager but was told that he is not available today.<br> If this is the way Vodacom treat their warranty obligation, then I no longer want to be a customer.