No "limits" on contracts

I took out a contract in 05/2015. Requested a R200 limit on the account twice, as it was for an employee. Was confirmed that it was in place. All went well. Never received an invoice/Statement. Last two months, the account is R1300!!!!!! Called in. Was told it is a "system" and they can not guarantee the limit. How can Telkom, Mtn, Vodacom cut off so effectively each time then ?? What is the point then ? So all of us can have a R2000 account each month ????? Find this totally unacceptable !!!!!!!!!!!!!!!!!!!!!!!!!