letter of demand - but service not used

I was debited in oct for an amount of +- 300 which i reversed as i did not know what it was for .<br> i then recieved a letter of demand for an amount of R579.48 from Esterhuyze Inc stating i agreed to this .<br> <br> i did call and enquired but never used there service at all but they want to charge me , forms were sent for me to sign on 21/08/2014 which i did not sign as i did not want to use the service.<br> <br> I have sent a mail to Esterhuyze Inc and informed them about this but with no relief<br> <br> Please assist as it seems they are doing this to alot of unaware people in need of finance.