prepaid simcard reflecting contract simcard on Vodacom system

I was on prepaid and converted it to contract after it ran its cause I reverted back to prepaid but now everytime I want to make a sim swap I am told my line is contract and I have to buy a +-R60 sim card. I just dont understand how can't they fix that. they were able to change me from prepaid to contract but now they are failing to process my sim card back on prepaid and their system actually reflect the real status of my simcard.