Failure to cancel contract and being billed for data I’ve never agreed to .

In January 2020 , I went to vodacom to cancel a contract after I’ve mistakenly subscribed to 5GB monthly recurring data and paid the amount stated to cancel that specific contract because I have 3 contracts with Vodacom . I asked that they change the number to prepaid but they failed to do so . I’ve been paying for the third contract (the contract requested for cancellation)for the past 5 months and receiving the monthly airtime . Recently on my June payment they stated that they sent me 2GB on the 1st of June which I never received but they billed me for it .