VODACOM *****ING FROM ME

I would like Vodacom to get back to me ASAP before I stop using their network I did an airtime advance of two R5's same day in January, and their service fee should have been R1 or R2 but Vodacom sends me a message that I must pay R23 for taking an airtime advance of R10, I called the call centre more than once asking why must I pay Vodacom double the amount for airtime advance. the call centre consults keep telling me they will call me back none of them has called me back, am afraid of loading airtime on my number cause Vodacom wants me to pay double the amount. I need an explanation from Vodacom cause I cant buy airtime anymore and make calls on my number.