Unauthorised debit order amount.

I recieved an email on 21/07/2015 stating that my contract is ending on 31/08/2015.Knowing this I went into the branch and asked them I want to cancel my membership because I am moving to port alfred and there is no virgin active.The one guy behind the reception desk told me that i should keep my membership for one more month seeing that I will be traveling to east london allot,I agreed on the term that my debit order amount will be the same as previous months.As I woke up this morning I find that an amount of R590 is deducted from my account,that is almost 5 times more than my normal debit order amount..I did not authorize this amount to be deducted. I am awaiting your response asap!!!