Vanished data by MTN network

I have received my student data loaded on my MTN number, on Tuesday late afternoon 10 gigabytes anytime and 20 gigabytes night, that data was also loaded on top of a 5 gigabytes that was left from last month, only to find Wednesday I realised that data has vanished, I called customer service the lady Asiphe Msitho doesn’t know what happened she will escalate the matter. This happened last time, not sure of the date but about 2 months ago. I bought myself data from the same MTN network. It’s so frustrating this happens to you when you have put trust in a network. To be honest I’m very disappointed about this, now what about those who don’t know. I need a breakdown of how my data was used from them and reload it as it cannot expire in 24 hours, if that also happens I need to understand how. As it is now I don’t have data, and how do work my things out without data. And how do I buy again when I had data that was loaded.