Fnb bank disappointment

Fnb sent me a msg on 3rd of August on their app and gave me an option to pay my monthly account fee with my ebucks. I followed their instruction on my fnb app, and paid my monthly account fee. The 17th August they deducted the account fees aswell. I made calls, sent emails, I even went into bank to get my money back for my dubble payment that month. All other months previous to this was paid. No one could fix this problem. Today one of their agents phoned me and said I dont understand how it works. She made me feel like I was an idiot for not understanding how it works. The bottom line is if I dont understand, why did I pay my monthly fee twice, they took both amounts, and did not re-inburst me with either. But I am stupid because I dont understand how it works. If I dont understand why did they give me the option to do this, so what it tells me is their IT department did something wrong on app. So fact is, I paid twice for my monthly account fee. And they talk to me as if I am stupid.