Vodacom bad service

So a asked Vodacom to cancel my contract and put me on pay as you go.the lady said no problem and that was a year ago.they still deducted the money each month so eventually I changed my bank.Then they blocked my number 3 months ago, today I went to Vodacom vredendal and the lady put me threw to Vodacom customer care.I explained what happened and she put me trew to some dept collection company.I again explained what was going on ,then she said that I owed them money...Its their mistake now I must pay.I cant do anything about it.I have supported them almost 20 years now and im very disappointed with the service im receiving...I went back into vodacom vredendal ask them what Can I do and they said nothing,so I left.im still without signal.I cant phone them or they me.