Airtime balance still not credited

I bought prepaid airtime yesterday in the afternoon via cell phone banking around 18h10 via cell phone banking. The money immediately left my account, so I thought my airtime balance was topped up. I kept on checking my balance till I went to bed. I woke up this morning having received an sms saying my airtime balance was topped up, when I checked this was not the case, my airtime balance had not been updated. so this morning I have phoned numerous times to the mtn call center and I am being told is to check my airtime balance after 3 hours till now my balnce has not been updated.