Incompetence and Passing the Buck

I am an Fnb Gold cheque Account holder and on the 13th Feb 2016 and 8th March 2016 I swiped my debit card and made purchases to a company I regularly purchase from. On the 5th April 2016 I was shocked to see payments going off my account. Payments to that company, I called them to find out what was going on and I was assured by them that they did not initiate these 2 transactions and that I did not owe them as they had received their payment on the 15th Feb 2016 and 9th March 2016. I could not understand why these funds were only going through my account in April 2016 when I had purchased the goods in Feb and March. I was told by Fnb that the company that I had purchased from had only banked the money on the 5th April for goods received in February and March. This is not true as the company i purchased goods from assured me that this was not true and the problem was on my bank's side.How can Fnb be so irresponsible and who gave them the authority to go and do as they please in my account.I had given authority for payment in February and March not in April. These transactions have now put me in a financial crisis and i want answers,I hold u responsible as I have done nothing wrong.