Vodacom continues its scrupulous theft from clients

I'm am now incredulous at how something so simple can be so blatantly ignored. So I topped-up a data contract number with 10gigs once-off data (which cost more than my contract amount) because I was running low in the middle of the month. When the monthly allocation was added on the 1st the once off was bypassed and I started using the monthly allocation. When I queried this (as the once-off would be expiring within 30days) I was told it's a business decision from Vodacom & I would have use up my monthly (which is 30gigs) first & only then do I use the once-off or forfeit when it passes expiry date. So a company can not not allow transfer or repurpose or prioritize the data in these kind of situations?! I find it completely unacceptable & unfair that one now has to simply throw money down the drain because of a technicality that Vodacom simple isn't even bothered to explain fully or fix. Useless company that does nothing but exploit its customers....really poor.