German used spares scam

i paid R4225 for a cheve captiva computer box from german spares rustenburg , 20 waltervaal avenue , i found them through gumtree . when i received the computer box through postnet i found the computer box to be burnt , upon inspection i saw the board of the ecu was severely damaged and someone tried to repaire it . i immediately called german used spares and told them that the unit they have sent me was damaged and has been open before , when i received the ecu there were no warranty seals on it. I was told by a guy named Wayn that there are no warranty , guarantee on electronic car parts and if i opened the unit they cant replace it for me. I argued that i have complete video footage of the unit as when it arrived and when we checked the unit up and found that it was damaged, when i inquired initially about the unit i was told it has been removed from a running car, which certainly was a lie and a scam . I have a cctv footage to prove that. I am so disappointed as i am a workshop repairing a customers vehicle. German spares refused to replace or refund and told me they have another unit i will have to pay for it again. how is it possible that they are selling their items without testing or inspections. i need help from someone please because i am a small buisiness owner and i cant afford to take a loss like this .