X3 exploding window

I purchased a 2010 X3 privately in October last year from an owner who was meticulous. It was a one owner, with low km, a BMW service and RWC. In February whilst parked in my carport the rear passenger door window "spontaneously exploded". I photographed the damage, having never seen anything like it before and contacted the BMW dealer to book it in for repairs. I then began to search the Internet for possible causes of this and to see whether this is a common occurrence. I also contacted an automotive glass engineer who explained to me that this was most probably caused by nickel sulphide inclusions created in the tempered glass manufacturing process and the age of my vehicle corresponded with the time it would explode if present. 

I explained all this, provided photos and requested that BMW pay for the replacement as this was a fault in the build of the vehicle and not due to any other causes i.e. driver or environmental. On the Tuesday I took the car in for inspection the door panel was removed, most of the glass shards removed and the regulator and cables inspected. I was told the mechanics of the car were in fine working order and the window ordered. I was told there was still no reply from BMW. On the Thursday I took the car back to have the window replaced. I couldn't hold off as the car was not secure to drive and park in its current state. Again, I was told there was no answer yet and they took the car to service. When I went to collect the car in the afternoon I was told they had not yet heard and I had to pay $850 for the repair and submit an email for reimbursement. 

I was not happy, felt I had been treated like a fool, but had to pay to get my car. Still, I submitted my claim, again detailing all the information, photos and confirmation from the expert and, unsurprisingly, was knocked back for refund. One week later I am in the back seat of my car and wind the window down (first time) and back up when there was a "clunk" sound and the window wouldn't wind. I rang BMW the next morning, took the car in the day after that and was advised that the cable had snapped and needed replacing and should look at replacing the regulator too, cost to me $960! I told the service advisor that this could only be as a result of incorrect fitting of the window I should not have had to pay for and am speechless that they would deny any wrongdoing. I have received an email today offering me 10 percent discount on parts and labour. I have never dealt with BMW before and am in tears at the appalling manner with which I am being treated now. Can you help me please?