Warranty of the Drill Hummer

Some times last year July - August I bought Drill Hummer which they told me that its 3 years warranty. I even asked how do they deal if I lost the receipt and they told me that the best way is to use my debit card where they can trace the slip using that transaction. Now 2 weeks back I took it back to Builders Warehouse in Sunninghill, now yesterday they phoned me telling that they are going to charge me R350 to fix which I don't understand why do I pay for something which is still under warranty and they are not responding on this issue.