Telkom Balance insufficient

Telkom Balance insufficient

Every few days 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 1GB paying R550, that supposedly give me 3000 min Telkom to Telkom. I can't make any Telkom calls!!!! I have been to there shops several times. They just tell you to check your balance dialing *108# that doesn't work. I haven't used this SIM for several month's so how can my balance be insufficient after 1 call?? My number is ***. I am basically paying for a phone that I can't dial to any Telkom number. Please help