Paid double for one transaction

FNB has a tendency of debiting my account twice and when I complain they come with a story saying it shows once on their side, I went to buy stuff at Ackermans and I had funds in my account that I depleted on the same day, they go on their pending list and have their own balance, when I receive more funds in my account the same transaction that I paid fr on the 30th went off again in my available funds! I asked them to investigate but seems like they are sticking with their story, this is daylight roberry, in these difficult times it is honestly unacceptable!!!!!