Even with spend limit there is no limit how can they do this

I logged a complaint on my account as one of my phone numbers have a spend limit on but every month I get additional charges but according to call center agent not allowed to put spend limit on additional charges my question is what is the use of spend limit for data or airtime if you can bypass it with no limit what so ever. Was threatened that if I don't pay for it I will be put on black list and cut off. Telkom come on why can't you help me with this