Netstar overcharged me!!

I subscribed to Altech Netstar for a tracking device in November. I chose the Safe and Sound Early warning package for R199 p/m. Then there was silent from them and I had to keep on calling and facilitate the installation process, then finally the device was fitted. Came end of Dec, beginning of Jan and the debit order did not go off. So i then call the customer call center to check what was going on the gentleman who assisted me and told me that my 1st debit was scheduled of end of Jan, which was well and good. Came Jan 29th, they debited R359.48, this amount was not what i agreed upon nor was I informed that that the 1st installment will be more. So I call the customer call center again and the lady by the name Ziyanda took my call and assisted me advised me that the R160.48 difference in the amount was a December Pro-rata (which i was not informed about when i called with a concern that they did not debit in December). So i told her that I was never told about a pro-rata, she then advised me that she was going to request a recording to listen to the conversation i had with the gentleman when i called earlier in Jan. Then the was silence, i tried calling again to follow up on this, i was told about a credit person. Kept calling the customer call center, and I have been given stories every time I call. Its a bit concerning and worrying since i have a 36 months contract with this company and 1st month already there are issues. Highly disappointed!