Funds missing from account

On Saturday the 3rd of February FNB cellphone banking had a technical issue which resulted to my account being debited R400 for airtime that I dont want. i I have called them a couple of times and they've admitted that there was an issue on their system, but they now dont want to return my money even though the problem was on their side. How can they be trusted if they can make such a huge mess but not take ownership of the problem. I am seriously thinking of moving my account. I would suggest that you check your statement very well. I want my money!! They are quick to fine people on debit orders, but dont want to pay back when they misappropriate your funds !!