Vodacom fail to close my simcard contract since 2021

I have been trying to cancel my Vodacom account since 2021 but the service is very poor,in 2022 I tried to cancel again after they have sent me emails of demand and I settled what I owed,and the agent athat assisted me said she was fixing my account and extended my contract,thats when I called and wanted the manager and thay said they will get back at me that was since early this year they been sending me black statements and I thought it's canceled..then a month a go I got a whatsapp massage from sheriff demanding me to pay them I R350 I owed to fodacom I then send the sheriff the blank statement from vodacom latest one was from Jun/July ...the sheriff said will get back to me but nothing till now my credit score is ruined I can apply for nothing.