Still no response from Standard bank

I have a credit card with SB and they took an amount per debit order that they were not entitled to. After my first complaint someone phoned me to say that the refund had been done on the 20th of May already and that it is mg banks problem if it doesnt show. I have phoned my bank as well and theres no proof of this deposit. I keep phoning and emailing for proof of payment and no one responds to my requests. This is unacceptable since when do banks ***** our money. And now suddenly no one knows where it has gone.