Refusal to reverse funds

I accidentally bought the incorrect airtime on the standard Bank app. I wanted to buy R150 Telkom airtime but bought for Cell C. When I didn't receive the confirmation sms, I thought there could've been an error and went back on the app and purchased for a second time, once again (unfortunately) the incorrect airtime for the incorrect network. I contacted the standard Bank help desk and was first advised to sort this matter out with the service provider whose airtime I purchased. After contacting them, they advised me that this is a bank matter and needs to be sorted out by the bank. I then phoned the bank help line again, just for the consultant to tell me that nothing can be done and I basically lost R500 rand! It was a simple mistake that anyone could've made and I just wanted the money to be reversed, but it seems like no one could or wanted to help me. What I'm trying to figure out is where is that airtime that I purchased going to. As my cellphone number is still the same but I just changed my network from cell c to telkom. So that airtime disappearing into nowhere. I am extremely disappointed that no one can take the initiative and use common sense that and extras made and needs to be fixed.