I bought a carburetor

My sister kesiah bought a carburetor and a mechanism for wipers which we swiped for. Only to find that the mechanism is the wrong one and the carburetor is faulty and we took both of them back. They took the carburetor back for repairs and they told me to come back for the mechanism as it was late and they wanted to close the shop. So my sister sent me simphiwe with 2 receipts attached to each other, an Indian gentleman separated the receipts and and only gave me a receipt for the mechanism only. So kesiah visited them today to fetch the carburetor she asked for a copy of the receipt as she does not have one, for incase the carburetor is faulty again and she can have proof she bought it brand new but they refused to give us a copy and said it's not their problem anymore and she must change her mechanic, so she must just take the carburetor without proof of payment.