Debit card Disputes-unacceptable

The ***** department phoned on Friday but due to myself driving the lady never phoned back, and then this morning when i checked my work emails i recieved the response you will not be able to assist as i authorised it? i did recieve a OTP but never entered it anywhere as you are suppose to do. And how must i make contact with the merchant if i do not know whom it is nor did i order anything online so please tell me how must i contact the merchant. This is totally unacceptable, i work hard for my money and for FNB to just shrug their shoulders and then place the blame on me for something that was clearly a fault from their side is not working for me. Myself and my whole family is considering rather taking our business & money elsewhere cos this is unacceptable