Defective fridge and bad aftersale service

My dad bought a new fridge at best home and electric in april 2021 and since then the fridge has been freezing in the cooling (the top part)section wich means all our veg is frozen and it then melts wich then leads to was accumilating in the bottom and everytime we go report it to the store manager she sends the driver to come and check it up until January 2022 when they took it for repairs and it came back on the 23 february 2022 still having the same problem and now the store manager blames us saying we are tampering with the fridge thats why its icing in the cooling section now they are threatening to cancel the deal and not owning up to the fact that they sold us a defective fridge and noe they harasing us for payment when we always pay on time mind you my father is 67 and in a wheel chair this is causing him unessecary stress as he is not in good health please help us resolve this matter even their head office is playing with our minds saying all fridges ice in the cooling section.