Vodacom Does Not Cancel when requested and then threatens you

My wife and I relocated and wanted fibre ta our new house so we both phoned Vodacom . We noticed that we app**** on both our names so one of us should cancel . I phoned vodacom to inform them that I need to cancel . We have great fibre at our home but I am very disappointed that after 4 months they phone me to tell me I am outstanding on my vodacom account with almost 3000 rand . now I am struggling to call them to get this resolved and being threatened that they will black list me. Not good Vodacom not good every time I phone I get told I am being recorded so I asked them to go and check who did not cancel But they say i need to call again and again to cancel , is my problem again! This is making me think if I still want to remain at Vodacom ?