Wrong airtime purchase

I accidentally purchased online a R16 airtime meant for MTN. The number I inserted is correct but instead of choosing MTN, I chose Cell C. The money was subsequently debited from my account but I wasn't credited with airtime. I phoned my bank (Standard bank) and they said I need to speak to Cell C for a refund. When I called Cell C customer care, they said there is nothing they can do. I then called MTN and I was told Cell C has been credited with the R16 and should be able to assist me. I was just wondering, if this was an amount like a R1000, would they not assist? Please help.