Wrongly billed and bad customer service

Hi, i have been with vodacom for a very long time, and i have recently upgraded my phone to an iphone 6, however for the last 2 months vodacom has been incorrectly billing me higher than what i should get billed i have been billed, the contract amount that i signed for came to a total of R358, however vodacom is billing me R578.99 for this and is charging me for 2 handsets which none of the 2 come to the amount that i signed up for as well as charging me higher for the top up R200 than agreed upon , i have phoned in and tried to get this resolved with no luck at all, they said they even logged a service call and will get back to me in 48 hours yet it has been a week later and i have had to feedback on this as yet, this is very frustrating as i cannot keep getting incorrectly billed every month without a resolution, and i cant keep phoning into to vodacom cause it seems like no one is helping to resolve this problem