Airtime reserved

I've been having a problem with making a phone call from the 8th of August 2020. I have airtime on my cellphone number however it keeps telling me I don't have enough airtime to make a call. I'm quite disappointed in MTNs call center it seems like Noone knows what they are doing each person tells me a different thing. I'm a loyal MTN customer and with this type of terrible service I will be canceling my contract and moving to Vodacom once my contract comes to an end. All I want is to make a call using the AIRTIME I HAVE PURCHASED!!!! Really terrible service from call center agents they don't know what they are doing!