FNB banking app security doesnt work

a transaction was processed on my FNB card and as per FNB's so called security measures, the request came up on my FNB app to approve it. I DID NOT approve the transaction and yet the transaction went through. I tried five times to get an answer from FNB as to why the app exists if its pointless and they avoided the question. They obviously do not want people knowing that it's useless