Makro sells defective products and withholds refunds to customers

On the 4th of August 2021 I bought an office chair via Makro's online platform and they delivered to me a defective product. I then reported this to them and they collected the product and confirmed that they will refund me on the 31st of August 2021. It is today the 19th of September 2021 and my refund has not been processed, despite numerous attempts speaking to Makro via email about it.