over charged

I recently took an upgrade with Cell c and I was happy with the amount I was give at sales stage, Last week I called client service to check how much will be my debit order for this month and I was advised it will be double the amount I was that I agreed up on sales stage, and I asked whom should I ask for this billing and I was advised that they will log a call as they normally say and they will get back to me with 24hours of which m still waiting for them to get back to me with feedback