Beware - hidden costs when signing 24 month payment plan

As my 24 month payment plan was ending on 28 June I called multichoice on 25 June to sign up for another 24 month payment plan at R879 pm. On 25 July I received an sms stating that my next debit order would be R 1064.64. I called customer services the very same day and spoke to Demi who confirmed my debit order, according to her system would be R879. I asked why there was a discrepancy between the sms and what she was telling me and she said she did not know. I asked to speak to the supervisor and was placed on hold. I remained on the phone for another 5 minutes and then dropped the call. On 28 July the debit order went off for the amount of R1064.64. On 30 July I again called multichoice and spoke to Thomas who could not explain the amount for the debit order and said he would escalate to his boss and also to the explora team. He gave me a long reference which later proved to be useless as nothing was done to resolve the query - Ref ********** 9-I124. He also said somebody would get back to me by the end of the day on 31/07. On 01/08 I called again, this time speaking to Ntombi who tried to explain that I was billed pro rata for the new 24 month contract as it started on 25/06. My contention is if my original contract ended on 28/06 and the new one started on 25/06, why am I being billed twice for a 3 day period ?