Preply Charged Twice for the Same Course, Refund Awaiting

My card was charged twice for the same lesson on Preply, which was a bad experience, unexpected also...Even though I contacted their customer service and was told that the problem would be fixed, they have not responded or taken any action. The delay in fixing the problem and lack of communication is very upsetting and seems like a form of theft. My money has been taken out twice without a clear explanation or solution, which makes me confused and angry, the way they're not taking this seriously is driving me crazy...