Charged on incorrect electricity meter

Hello I need advice on how to deal with Only Realty Helderberg. I was living in one of their Cape Town rentals for 1 and a half years and for the better part of this lease I was being billing on my neighbours electricity and water meters. I started complaining about my high bills early in the contract but they insisted it was correct until they found a fault then fixed it by swapping the wrong meters again. They only managed to correct the meters by around September last year and to date I haven't been reimbursed what looked like R6000 that I was overcharged. There seems to be no remorse or urgency and I feel like pulling my hair out trying to get feedback from them. What are my options?