Mr D and their unprofessionalism

I ordered a few things yesterday from Mr D, when I had to checkout it said an error had occurred on their side but still proceeded to deduct money from my bank account. They have asked me to send a bank statement of which I did, they then asked me to send screenshot of the transaction. How much longer should I wait until they refund me my money and I sent proof of it but they still give me the go around. This is not on, as a payee I don't deserve the treatment from them. They should be professional and do the right thing. I'm not happy at all. Please, I need help