Hidden Costs

On 28th December 2015 I got a contract phone fromTelkom Rosebank and I was not told (whether in writing or verbally) that there was an extra cost to the contract. All I was give was an invoice written R0 and told I'll get my next statement in January. Now all of a sudden I get the statement and I am expected to pay R750. 50 whereas I agreed to a monthly payment of R399. This is unacceptable! The consumer protection act states that all costs should be stated to clients. I never agreed to an additional R305. 50 which I was never told about. I refuse to pay this extra amount as I was never informed about it.