UNAUTHORISED DEBIT ON MY ACCOUNT!!!

I have been a loyal FNB Account holder for the past 21 years. To my dismay, this month, a company that I know nothing about, sagepay, deducted money from my account. I got their contact details from online banking and they told me that this debit was from a company called perguson. They gave me perguson's contact details as they said there was nothing they could do from their side - that I had to sort this out with perguson themselves. I tried perguson's number but much to my chagrin, the number does not work!I called back sagepay and they were adamant that this was the only number they had for perguson and that they could not assist me any further. FNB I am not about to lose any more money than I already have because of this unauthorised transaction. I know full well that you would not be willing to lose a cent yourself if someont stole from you. This is *****ING! No if's or but's about it. Please see to it that my account is refunded with the amount that was debited from my account on the 01.04.2016. I await your positive feedback herein.