Airtime reflection

I am furious right now because I can't buy data. Every time, I buy airtime the whole amount doesn't reflect immediately (only a portion of the amount that reflects) it takes hours for other portion to reflect, I have to buy more airtime than what I need, I don't know if that is a tactic to get me to buy more airtime. I have contacted MTN regarding this but nothing was done because it still persists.