Alerts terrible customer care

I have bought an clutch kit from the alert engine parts Port elizabeth branch. After fitting the part the car did not function the way i should, after futher inspection we saw that the clutch kit they provided was faulty parts. So we had to strip the parts out again which has taken alot of time from myself and customer. I have taken the parts back so they can have the oarts checked out as which they confirmed the parts are faulty. Now they decline my claim for this part even though they did confirm that it is faulty. We have returned this part within the first 3 days after purchase as we had to get the car done. Reason they dont want to refund or take my claim is that they say i need to provide a copy of the perchase receipt which i dont have anymore. They have all my details of when where and for how much it was bought for on their system so why cant i be refunded ifbthey have the proof of the payment which it was done by card can someone please help me with my situation?