WRONGFUL DEBIT ORDER

Unauthorised debit order from my account! I phoned in March to cancel my month-to-month contract, this was done over the phone. No documentation was sent to me but I assume my last payment would be in April. The debit order went off on my account today HOWEVER it was for R799. Before cancelling I moved over to a R599 month-to-month contract from a R199 contract because I do not have Vitality anymore. In March I was still charged R199 so this charge of R799 cannot be explained. According to Payment association of SA, it is ******* to debit an amount off my account without my knowledge or consent. I cannot get through when I call either - multiple numbers to the same call centre that does NOT pick up. I want my money back.