Billing cannot be correct.

Good Day<br> <br> Please advise why my account is so high.<br> <br> Im used to paying R99 per month. In august last year I was sent a very high invoice and now again for March.<br> How is it that its a steady R99 then all of a sudden a jump?<br> <br> I use WI-FI at home and my office and my device is only used for emergency's like when im not at home. <br> Furthermore sometimes when using the modem I don't even get a connection.<br> <br> Vodacom I just don't understand this. I have not exceeded 4 gigs of data.