Vodacom — contract why should I still purchase talktime???

I have a samsung s6 on a smart s package. 7 5mins, 200 sms and 250mb data. I've realised now that the minute my free minutes are finished I am unable to make any calls from my phone or use cellphone banking. The error I get says insufficient funds and my calls just end... Not one consultant can help me!!! Why should I have to purchase airtime if I have a contract??? This is becoming very frustrating.. It is not a device issue as I have tried to explain numerous times. Can someone please help me with a solution!!! I refuse to have to purchase the talktime if I have a contract phone.. A gentleman by the name of daniel has been trying to assist me as much as possible... But I need to have the problem sorted asap.