Shifting the goal posts

I have setlled my Woolworths account. I overpaid by R1000. They charged me some interest and claim that I only overpaid by R800. I requested payment into the account from which I have been paying the account for over 10 years. I sent them the absa beneficiary list that shows payments I made to them since 2015. This shows the amount, date and time and the account from which they were made. I also attached a copy of my ID. I followed up today after 7 days of settlement. Now they want a certified 3 months bank statement before they can help me further. What a ridiculous demand.