Bad refund policy

I have settled my Makro account and closed it, and Makro realised that they have overcharged me on my settlement amount and I am intittled to a refund of R550 and in order for me to get my refund I need to draw a bank statement of which will cost me money, and I can't understand because it's on their system that they owe me the money and it was also their fault that a double payment was made, and now I'm told I should write to them explaining to them what they did wrong, I really feel it's very unfair and seeing that I have been their loyal customer for all this time.