Contract and Billing Issues

We went to MTN on the 30th June 2015 to renew the contract of two phones, and one new addition. All these phones were previously on top-up package, which we indicated to a clerk at MTN, and we also suggested the 3rd phone to be on same package. In July 2015, all three phones were freezed, they could not be used, and one cell phone had a +-R3900.00 bill it. On consultation, we were told that this was because the user had over used it. I couldn't understand because the package was top-up (which means the user must pay from his pocket to have data).We spoke to station Manager, Shavaughn on several occasions, but she couldn't resolve our problem. So much time and money been spent trying to resolve the issue. Shavaughn couldn't clarify why top-up package could result in thousands of rends per month.We went to MTN Head Offices in Fairland's, for complain and after studying the account, they picked up that my contract was actually changed to another package without my knowledge, and they advise us to go back to Boksburg branch to rectify the error, but Shavaugh said a BIG no - despite the mail sent to her on 16th Oct 2016 by Head Office. As it stands, the phones are non-functional.