Exorbitant billing always happening a couple of days before the new month

I am at my wit ends with vodacom and there incompetence billing system!!!! Every month my bill will sit an amount that I find reasonable, I always make sure I have a data bundle in place so as not to incur out of bundle data expenditure. Then 3 days before the end of the month before the new billing starts all of a sudden there is over R1000 added on and it claims to be out of bundle data usage ! I dnt even use that much data in 3days, I find it funny that i only seem to use a R1000 or more of data in the last 3days of the month Only but the rest of the month I dnt even get to a R1000 in data bundles for the 3weeks before. I am sick to death of raising invoice disputes because then u ***ardly send me an email telling me you have investigated and it seems to be correct. DISGUSTING you are actually falsely billing me and taking my money... and without fail again this month I am sitting with a bill I didn’t expect because when I checked a few days ago it was a R1000 less ! I will be canceling my contract and going somewhere else because only vodacom does this to there customers. Also I am not the only one experiencing this nonsense so it won’t be long vodacom till all your customers leave you at this rate. Absolutely appalled !!!!!!