Samsung refusing to return my mother board which they damaged

Good morning.please can u assist.I have been having an issue with samsung head office since October 2017.I had taken my samsung s7edge to 14th ave on the 21.10.17 for a cracked screen. I was registered for the free adh screen repair for damage within a year.samsung sent me a qoute for over 10 000. Rand.I refused to pay as I am registered for a free repair.they requested a p.o.p which I furnished and then they swnd me a qoute for over 6000.rand claiming damage to the mother board.there was notjing wrong with my board so I refused to pay this as well bcos when the technician took mh phone in it was working perfectly fine with exception to the screen.samsung refused to repair the screen and I said to give my phone back to me In the condition that I gave it to them.I collected my phone on the 27 November 2017 and realised when charging the phone that there was no mother board in the phone.I immediately called samsung and spoke to shaun who assured me he would hand over this issue to his superior. ..I have had no joy.after a week I call shaun again and he advised that I go to the head office and seek assistance. In January 2018 I go to headoffice and spoke to taariq and explained the entire issue.he goes to the back and comes to me confused and says he cang see any mother board there but maybe they can give me discount.whh should I pay for something thag was nig damaged in the first place and why haveng they returned mh mither board.samsung is not helping me one bit even after I advised them that I will take this further. ..please can hello peter assist me un this regard.