Incorrectly invoiced and now handed over!!

I was using Vodacom fibre until April this year. I got an invoice for R1500 that I asked to be rectified because the 1,5 was not calculated correctly. No one is assisting me. Instead, my account was handed over and still no one wants to explain about the 1,5. I will not be paying for additional months when I didn't have the fibre anymore. Can I please be assisted because this is tarnishing my credit record!