Loan I did not apply for

I have been receiving calls and sms from Fonchoice offering me loans but I never took any loan from them. This morning an amount of R15k was deposited to my account I called them to report this and they refused to email me banking details and insisted that I take them telephonically and pay. I found this strange and the lady refused to email banking details in writing and also refused to transfer me to her superiors. I explained to her that i need to have records for this hence I requested an email. I sent an email to *** but there was no response. I an now stuck with R15k in my account. This is *****, they have no right to give me a loan I never app**** for and refuse to email banking details for me to send it back. I don't know where they got my account number from all I know is that now I am stuck with R15k.