Vodacom is a *******

Vodacom is a *******. Every month on my statement there's an additional amount. I queried this months ago and I was told it's airtime advances that I did not pay in time but to my surprise whenever i bought airtime they would still deduct and again on my statement. I called again and asked they told me it does happen that clients get debited when they purchase airtime and on the statement, i must log a call for refund so I let it go cause ddnt have time for these long process. So last month i took airtime advance on two numbers and on the 31st purchased airtime for both numbers. Now today my statement says I owe R1909 and some cents instead of R1850 and some cents. So I call Vodacom now at 10:11am the lady gives me a brakedown on my sons no and tells me there is R30 something rands airtime advance owing. Im shook cause i did buy airtime the lady tells me its for February. Im like why uts debited now and not on March and y ddnt they take it on the airtime i purchased. She says that's how its done. And then she tells me on my main no i owe R3 something for data in feb i have been purchasing airtime why was it not deducted then or in March invoice she says that's how its done. I am not happy about this cause I was told if i take airtime advance it will be settled on my next airtime purchase or invoice.