changing my monthly fee as they pleased

<p>I have a Telkom Account, where I had purchased a phone and went on to upgrade! The monthly fee agreed upon was R599 ! That is what I can afford! Nothing more, eapecially for a cellphone! Within 3 months of the upgrade, i noticed that the amount deducted on my account was now close to R1000 ! When i called to querry they to sudden increase, i was then told that an sms was sent offering the change etc. I notified Telkom that I had not received such an sms and also I have not agreed to such a charge as i cannot afford it! I was then told that no response to the sms meant that they could go ahead! I have been fighting for them to correct this issue and told them that i have reversed the monthly deduction and paid the original amount agreed upon! But they are adament that I now have an outstanding balance which is the amount I had not been in agreement of! What do i do going forward! As they are making threats to block my phone but I have been paying the monthly fee which was communicated to me(R599)</p> <p>Please help!</p>