Sim still not working after loaded with 3G data

My sim card has worked yesterday. I then loaded 3G data for R 299 but yesterday evening all of a sudden my sim card was no longer on the network????? How can this be???? I've just loaded 3G data yesterday? I then phoned the call centre waited for almost a hour then she said that I need to load airtime. I bought a R 29 airtime voucher but I can't load it. If you dial 100 is says number does not exist. Also can't load with *100*01* etc. PLEASE ASSIST. I need to connect to the internet this is why I've bought the voucher!!