No Help with Remedying THEIR mistake with an Order

I am very disappointed with Netflorist. I received a R250 voucher from Vitality and that is the only reason I decided to treat myself with a plant from Netflorist. I chose a Monstera Deliciosa and with shipping, it totalled R329.90. I put in my voucher code and the price dropped to R79.90 - which I could afford. When I made my Credit Card payment I was charged the full amount. I could not find a way to do a reversal, so I emailed them immediately explaining the issue. I sent them the voucher and the invoice from their site. Their solution: They cannot give refunds, they will give me another vouvher. I am so upset, I did not really have that money to spend as times are so tough for us all, so I would have NEVER bought the plant without the voucher. THEIR site is in error, but now I must suffer! I also emailed them immediately, so if they responed more timeously, they could have reversed the order - if that option is available on the website, I could not find it.