Being charged for incorrect contract

I did an online order during Black Friday for the 20 gig day and 20 gig night deal at R199pm, this was activated on the 15th December. When I received my invoice at the end of December, I'm being billed for 10 gig at R326. I have been moved from pillar to post because NOBODY wants to take responsibility and change this before my account gets billed incorrectly. From customer service, was taken to billing, then new sales, then renewals. Finally I was able to speak to Lebogang Tswale who was able to give me a manager's email address. This service is appalling, there are notes on the system but nobody cared enough to just escalate this.