outrageous billing

I got my company phone on a smart L package and well I wasn't informed that I'll be paying once my data is finished! In fact how is it possible for one person to use R17000 data? IMPOSSIBLE... once I emailed vodacom regarding this, a new bill came down to R45 but i was still doing everything that I've done in the previous months.. . now I'm still paying off the outrageous bill... when i started investigating i found that there were numbers phoned late at night that i don't know... when i phoned the numbers, complete strangers picked up. Explain? If I can find out that I'm paying a bill that's not mine and data that i didn't use, I'm demanding all my money back...