Data just disappears

I have a contract that I pay a small fortune for every month, I get 6 gigabytes every month. Today, a week after it reloaded I get a notification that I’ve used up 80% of my bundle, when I check the MTN app I’ve only used up 0.88gigabytes of the 6gigabytes. When I contact customer care I get told they CAN put in an investigation but I must check my app to see what data I’ve used. After pulling teeth I get them to lodge an investigation and get told that it could take 2-48 hours. In that time my data balance drops from 2gifabytes to 500mb and the agent just isn’t bothered that I’m on WiFi with my data turned off, I just get told I can use the remaining 500mb while I wait for someone to investigate. It’s absolutely atrocious that I’m being put in this position where I’m basically being ****med to buy more data waiting for an investigation that may or may not happen.