Insufficient airtime message when making calls

This week I had bought minutes and airtime but when I try to make a call it says insufficient airtime to make a call. I recharged airtime again same issue, I called customer care they told me I should switch it on en off wait for some time. I did that and even put my sim to another handsets.

Nothing worked and I kept on call customer care some they promised to get back to me. Some said they don't see the issue on their side. Am so annoyed I need to make important call I can't. Can u fix this asap or I should just port to Vodacom.