Cell C service not working

I keep running out of airtime. I have tried 4 times to increase the limit on my two business cell phones. I have been to cell c store twice, phoned the help line and contacted the agent who originally sold us the contracts. Each time there is some long story about why it is not working, but it does not get fixed. Out of frustration we asked to change the contract to something that works. After writing an email and getting the paper work in order, we are supposed to be able to top up using the usdn code. But that did not work either. The email asked specifically to activate the usdn service so that we could top up. Now we get told we are not on contract or on the usdn system. Tried purchasing through the bank, also does not work. Nobody can fix it either. We are sick and tired of this service. No-one at Cell C seems to know what they are doing?