Cell C can't reverse or refund airtime?

Cell C operators tells me that airtime cannot be reversed? By accident I bought R 1000.00 worth of airtime instead of R100.00 through my banking app. I went to the bank to ask if I can reverse the airtime and they told me to contact Cell C. I know that I'm not the only person who made that accident, so there must be a procedure to reverse of refund the excessive airtime?