Telkom is *****ing from my account

I bought an iPhone 6 plus 32GB online from Telkom for R449.00 per month. They have been debiting R499.00 from my account per month for the past 13 months or so. I have raised this issue several times of which hey always give me a reference number which they close after several weeks without resolving it each time i raise it. Is this fair business practise. Telkom is literally *****ing R50/month from my account.