Major Billing Error

Retired telus customer service rep. We would know why the $1000. We would check it one of two ways. 1st check for any billing orders (they disappear after a time frame)if not take a look at differences between bill and products on the account, then we tell you what was found.  Usually on a bill there's a description by the charge and you haven't said what it shows.  We look at comments on the account plus known issues.  We are supposed to do a case for follow up, we give you the case number.  Cases are handled by the ordinal rep and if not available then case assigned to another rep. If necessary we have a internal system were we can ask them to look at  a account as a double check. I had a very high credit limit I could approve as I had 28 years experience.  Sometimes the credit is too high even for me, then a manager needs to approve.  I email the manager to look at the credit and put there ID in the notes on the credit,  in the comments on the account and in the case. The rep needs coaching,  99 percent of the time I can handle in one call. Definitely not handled well