Faulty decoder

Good day My father bought a decoder from one of the pep home stores at Dobsonville mall now the problem started when i was suppose to register my decoder with multichoice and thy said the decoder was faulty and i should return it to the store, i got to the store to ask if thy can Exchange my decoder i was asked for receipt i told them i lost my receipt but i just need to exchange not refund they totally refused. I then went to the store and ask what was the reason for not exchanging the decoder i was then told that without a slip thy wont be able to do so because at the store they don't keep records of cash transactions and i just lost my R600 just like that wich is impossible i need someone to intervine on this matter because i am disappointed at the store manager for giving me such an answer her name is Lindiwe from Pep home Dobsonville.