Motherboard Samsung S8...passing the buck

My phone was booked in for repairs. a quote was given after my enquiry I was informed the mother board gave in. I tried to get hold of the technician and was promised he phoned back since Wednesday the 18th of October by the manager of Cresta Vodacom. Today the 23rd of October the technician phoned and informed that the warrantee is cancelled due to the cracked screen. Tonboni was very arrogant and did not give time for me to explain anything, and not helpful at all. My question was I upgraded the contract in April/May 2017 how is it possible for a motherboard to crush within 4 months of purchase. He did not answer my question and was focussed on the cracked screen, Nor the service department nor Cresta Vodacom can give an answer on the motherboard and what is the reason for crushing How can a mother crush within 4 months . what they implicated is if your phone fell the motherboard will crush. If your screen cracked your motherboard will crush. Isn't there perhaps a default in the motherboard of the S8 Samsung phone that they doesn't want to admit as the defualt in batteries from the S7 phone's. I want the phone to be replaced . I will never recommend a Samsung phone ever to anybody