was the injectors replaced by RMCI approved work shop? get them to provide you with a technical report with copy of there RMCI registration certificate despite having 183000 Km is quite a bit, but as a rule the pistons should last longer than that.
Submit this to the insurer and send a complaint to the relevant insurance Ambuds man. I just wonder if the guys that fitted the new injectors did not maybe dropped something into the injector hole and it maybe moved from the center of the piston to the side and the when it hit the head it pushed through the piston.
Is it an extended warranty that you have, and read the fine notes.
But it is typically of insurance they will gladly take your monthly premium
and when it comes a claim the will do there best not to pay.
Medical aids are just as bad these day.