Wrong upgrade

On the 7th of January, at 10h29, I upgraded to the 20GB Data Price plan Top up with Bonus Video Ticket 5GB (R199/m for 24 months) plus 50min Monthly Recurring Voice Bundle @ 75% Discount (R15/m for 24 months) plus caller ID. In March I've received an invoice for R332.99. I’ve stopped the debit order because the contract was not what I've app**** for. In May I’ve paid my arrears for March and April and the amount due for May totaling R671.97 because if my account was correct I had to pay R223.99 each month which I've paid since then. Despite all my calls and e-mails, Vodacom continues to insist on payment of the arrears