overdraft made available without my permission

I just recently find out ive got an overdraft that I didnt even sign for or request for that matter..on the 7th of august I accessed a temp loan via cell phone as I needed extra cash..apparently I could have pressed the overdraft option by mistake. .who made that decision of making overdraft available on my cell phone banking without my permission as I had declined it on the day that I app**** for my cheque account.so far on the system it shows the overdraft was app**** for via Internet banking, which I dont make use of or remember user name and password for that matter. Disappointed