Reversal of charges

On the 27th of September 2018 at 06h42 an amount of R1 422-85 went off my account. Immediately when I received the message I phoned FNB to cancel the so called “purchase”. They cancelled my card and I had to submit a “cheque and debit card dispute form”. I submitted what information I had of the purchase but FNB sent me a sms that said: “We are unable to process your dispute. Please resubmit together with the required communication with Merchant / service provider, requesting refund and cancellation.” The FNB message I received that morning of the purchase read “reserved for purchase ********** how can a purchase take place If I didn’t input my pin or received an OPT from FNB? Please note that when I called FNB the purchase was still on my pending list. I would like to know why a debit order can be reversed FORTY DAYS AFTER being deducted from my bank account but not a purchase that I didn’t authorize or get an OTP pin for? When I googled the company name on the purchase notification and it’s a company located in US. FNB call center expects me to make an international call and ask the company to reverse the purchase. Firstly do they know how much and international call will cost, secondly tell me how do I phone a company to reverse a purchase without a reverence or purchase number? Seeing that I didn’t purchase anything and called FNB when the transaction was still pending I don’t understand why they can’t reverse the charges like they do with a debit order?