Horrible NETWORK

Im appauled. There is a advance airtime service that we probably all use. My limit was recently increased to R50.00. But now when i check the balance it says i owe R75.00 and yet i had bought airtime to decrease the balance. How do i owe R75.00 on R50.00 limit or you have overdradt advance? it doesnt make sense and i know i dont owe more than R45.00 as i loaded airitme. No wonder everyone is moving to TELKOM MOBILE because your service sucks