Matrix Warehouse ****mers

I bought a charger from Matrix , which turned out not to be the problem , I returned the charger within 7 days , now they don't want to return the R1000 they charged - they want to give me a store credit . What am I supposed to do with that ? I don't have the extra money to fix my laptop . Just return the money - nobody told me I cant return the product to get my money back