Untrained staff and cannot resolve a simple query

Please train your frontline staff to under the difference between a debit and a credit! My phone is out of of contract so been happily paying a reduced monthly rate. All of a sudden on the 3rd January a HUGE DEBIT ORDER goes through my account and no one can explain it to me. Been to three stores and the contact centre at MTN head office where Twani had absolutely no clue what was happening except to say she will log a query. Three have been logged over a week and NOTHING has happened. I now want to convert the one contract onto prepaid and the consultant tells me it cannot be done (Northgate) until the query has been resolved. Twani (MTN Head office) does it but from the 1st June???? It is out of contract so why can't it be done right away? The excuse now is everyone is working from home that is why there is a long wait for assistance. Really!!!! Obviously staff training is just not happening at MTN. And by the way, still waiting for assistance. A week later.