Disappearing of airtime and data

On Tuesday around 3pm I had 22MB of data, R23 airtime, 13 minutes of calls and 336 of SMSs. Around 5pm I try to call my husband and it says I have no airtime to make a call, and wen I check my balance it says 00 for everything except for SMSs. at 17:30 I called MTN and they said I should not buy air or data for 24 hours so that they can find out what is going on,I did as they asked. After that call I only sent 3 SMSs and made no calls because I obviously did not have airtime. So yesterday, Wednesday, I called again as they requested after 24 hours and they say I made calls before and after I spoke to them on Tuesday. The only call I made was on Tuesday at 14:47 and lasted exactly 19 seconds. So how do I make calls on Tuesday after 5 knowing I don't have airtime and I could not buy it for 24 hours. The lady I spoke to was rude and when I asked is there anyone I can speak with regarding this matter she basically said sorry but we cannot help you!! This is not the 1st time this is happening to me and I do not appreciate how my matter was treated. Last night I bought R10 airtime to call my mother. I spoke to her for about 5 seconds and my line was cut saying airtime depleted