Inferior product to be exchanged

It irks me that I have to use this platform to get an issue resolved. However, I have mailed then with no response, sent a Whatsapp to their Whatsapp account with no response, mailed a parent company with no response. My problem is related to a 40000mah power bank I bought that can only charge about 4000 mah. I need this exchanged for a product that actually works.