Over billed

I was invoiced R986 and my premuim is R204. They say i chose to recieve notifications. Fair i did that but iv never recieved those sms notifications. So why bill me for a service i am not recieving. Their explination of why i never recieved the notification is because i ported my number from mtn to cellc. I have had this number for more then ten years and its been on the cellc service for that ten years. And when i took out tracker my number was on the cellc service. I have called and queried it for over four times and im still not getting helped