Eating my airtime

I keep getting a USSD message saying that my data is depleted. When this happens:<br> - *141# tells me I have +- 1.7Gb of data left!<br> - It has already eaten into all of my airtime, leaving me with a R0 balance<br> <br> So either:<br> - *141# doesn't work properly <br> OR<br> - You are billing me unfairly<br> <br> Please sort this out! I use this phone for work, personal AND to run a second business. I *cannot* afford to keep running out of airtime/data because your billing is broken!