Network problems

For the past two months almost daily I have been a unable to make calls even though I have recharged and have airtime. Everytime I to make a call I get an 'you have insufficientvairtime to make a call'.<br> I have been calling the call centre and simply told they have refreshed my number and that i should switch off my phone and it should be fine, needless to say this does not work and im always back to square 1. This is really frustrating now and there seems not to a long lasting solution from MTN.