Unsatisfied with service

In April 2019 I took out a contract on a Mini Wifi. R149.00 per month for 8 gig in the day and 8 at night. Since the start of this contract they keep on deducting the wrong amount of money every month. I've been phoning every month since April to have this rectified and pay the extra money back they deducted. Each time I speak to a different consultant and each one has a different story and does not help me with my problem and I just keep on loosing money. It was said it will be rectified and my money will be refunded. And they will make sure that the right amount will be deducted. But I'm still waiting and the same happened again and again. Up to now. I've been a loyal customer for many years and I'm very disappointed with Cel C,and will definitely consider to not renew any of my agreements in the future.