iStore has owed me R20,000 for a month on a double billing..!

This complaint isnt levelled at the store itself - they tried to assist - to a point and haven't returned my last few correspondences, it must be said..its not about naming and shaming the branch... iStore owe me R20,000 for a double billing. No feedback ! I chase and I chase and nothing. I've taken them evidence from my bank statements and still nothing - isn't this just completely ridiculous !!