Being billed for unactivated account

On 20 August 2015 I app**** for an ADSL line from Mweb. After a salesperson called me back we completed most of the application, however when it came to payment, I declined to have a debit order put on the account. The salesperson informed me that the account can only be activated on payment of R700 for three months subscription if I choose not to do debit order.After discussions with my wife, we decided that we will not allow ourselves to be punished in this way because we refuse another company access to our accounts.The salesperson did call me back and informed me that if the R700 is not paid, the account cannot be activated.Over the past weekend I received an SMS informing me that my Mweb account is in arrears. When I queried this. I received a username and password. Once I inputted this in the 10.0.0.2 website it informed me that my Mweb account is now activated.Now I am trying to get Mweb to do the right thing and adjust the invoice pro-rata from 12 September 2015. If this deposit was then so necessary to activate the account