Incorrect billing

I had a 24 months contract with Vodacom which l paid off in November 2019. To my surprise they debited my account in December 2019 & when l queried about this debit order, their response was that l should have given them a 30 day notice prior to the end date of the contract. Off which l was not in a good space to ask a lot of questions l just agreed. I then told the consultant that l lost both my phone's & will no longer be using them in the future. She promised to note it on their system. A week later l contacted Vodacom again to confirm if the contract & both numbers were cancelled/blocked as agreed with the previous consultant. This consultant promised l have nothing to worry about & they will not debit my account starting from January 2020. To my surprise again Vodacom debited my account for the second number. I only realised this after their 3rd debit order. My first contact this year about this query, was on the 23rd April 2020. I sent an email to Vodacom as it was a struggle to get hold of their call centre. They responded requesting some information for authentication which l provided them with. Few days later l received a call from their agent whom l told everything that went down. He promised to resolve the issue instead the very same month l received my billing from Vodacom. I've been sending emails since then, they sending me back & forth with no success. They gave me this ref nr: l***-7 which is not helping me with anything because everytime when l want an update about this query they would ask me all the questions starting from scratch & after l have given them all the information l don't receive any further communication. It's over 5 months now that l've been trying to get help from Vodacom with no success. I'm extremely frustrated & don't know what to do as they promised to hand over my account if l don't pay the amount in question.