Calls keep dropping while on line with Support Center

<p>Everytime i am on the phone with vodacom support my calls get dropped and then have to re-explain everything from beggining and go through entire process AGAIN! I am on Contract and my data bundles have run up, everytime i try to top up my data via the App or via logging in on internet from pc i keep getting error "insuffiecent airtime", When trying to get assistance they keep saying its because of contract, not knowing actual issue. and we can never get to root cause as calls keep dropping then have to start AGAIN</p>