Telkom Mobile *****ing My Data

I have tried to call Telkom but wait more than 20minutes every time and still can't get a hold of anyone! The issue I need to be fixed: I habe a 20GB monthly contract. I use less than 20GB every month, my internet usage stays relatively the same. This month I ran out. So I topped up 5GB for a whopping R300 thinking this will see me through. A day later all gone!? That day that I had the 5 GB wasn't an unusual days, they must be *****ing my data! How else?