Very disappointed service.

Every day when I try to make a call I get a voice prompt saying "Your balance is insufficient" even though I have a contract with them!! I am on Telkom Free Me 20Gig, they give me 3000 min Telkom to Telkom and 1500 min to other networks. My data works fine my minutes shows I have over 1500 any time minutes, it is really frustrating and every time I call the agents don't understand ,they are useless they aware of my query and do nothing about it,because of telkom I'm using so much of business ,this is unacceptable because I'm paying for a contract I can't use.