Hello MTN SA advertised a SIM with 20 GB to be loaded on monthly basis and promised to keep my existing number but when the SIM card came it has 1

Hello MTN SA advertised a SIM with 20 GB to be loaded on monthly basis and promised to keep my existing number but when the SIM card came it has 1.6 data loaded and it can't be SIM swapped. I called them several times , sending email with no help. MTN are ********