Refund still owed to me, 3 months on....

Ordered some goods online in March and both my credit cards charged 2 x each, but order not processed. Eventually paid via instant eft. Got refund on one credit card in April, but am still owed about R1800 on the other card. Have tried contacting customer care department by phone about 6 x (each phone call long delays and average about 20-30minutes!) and sent several emails with proof of payment... but to date still no refund. Cannot seem to speak to anyone who can help me. Taking the issue up with my bank now.