Incorrect billing and ruining my credit score

I took out router in 2015 and then I took out a cellphone contract in March 2016 , both not open ended contract. Then once of the Vodacom consultant contacting me in August offering package for the router as the contract was coming to an end. I told the consultant that I am sill happy with the option I am still on and Vodacom confirmed that they have cancelled the new option and the back to the old closed package as per commencement of the agreement.

Months went by, then Vodacom started debiting me higher amounts, which when I enquired with them i am being told that i have changed my package from close to open package on my both numbers. Now the system keeps debiting the higher amounts and as a results my debits bounce back, which it affects my credit score so badly.

I tried calling Vodacim couple of times now and i am being told nothing can be done until I pay the required amount and they will unblock my phone.

I never agreed to any changes.