MTN disappearing data and airtime

I had my son on a 500MB MTN contract and he is s student. UKZN allocated 20GB day data and 20GB night data to all students to start online lectures. The 20GB day data was given in 2 lots of 10GB each. The contract reached the end of term and I requested it be moved to prepaid. The agent confirmed that the data that was given by the university will still be there after it is migrated. When I checked the balance after it went to prepaid, 10GB went missing. I tried calling MTN but I'm getting a run around. I transferred R20 airtime to his phone as he was now on prepaid- even the R20 disappeared after a day. MTN, please don't ***** from us. Please replace the 10GB data and R20 airtime that belongs to us. Thank you