Vodacom forces me to pay for their mistake

Have cancel my Vodacom account/ contract in October 2023. However it wasn't done and was immediately canceled when I posed on hello Peter. The people I have spoken said it was a mistake on there site and will sort it our, and I don't need to worry any more. On Thursday 21.03.2023 morning an dedt collector from Vodacom called me and said I owe them money and when I told him regards the issue as above, he said short and sweet ''he don't care I need to pay " How can one person tell you one thing and the other person said another thing. Now Vodacom will probably put my name on the bad Credit list/ Credit record, because of the mistake and this is unfair that I must pay for their mistake or was it a mistake??