Irrepareable Iphone X - No explanationn

I am very disappointed about the service on my Iphone X. The initial problem was that the original Iphone charger explode in the phone and did not charge thereafter. Now they say the damage is that the phone was opened before it reach the repair store. I asked what is the root cause of the problem and they couldn't answer me. Only that the phone was opened prior. Now they want me to pay for a new phone!!!??? Why?? The phone is not even close to one year old. Cell C couldn't give clarity on what the initial problem is for it to be irreparable. Totally unsatisfied service with no professionalism and poor service!!!