Taking money out of my account without my authorisation

I had a great experience till they double charged my account for the same order and now you are not able to get hold of them to get my refund and it is not a small amount R570.00 I dont have that kind of money lying around for making mistakes. They dont respond on any platform and you can not get hold on a phone of any kind. How do they just charge my account without my consent or authorisation from my bank? That is *****ing to say the least