Toyota Financial Services not acknowledging settlement and victimizing me

I am literally being ****med and victimized by Toyota. On the 28th of February I settled the amount for my old Toyota Rush during a trade in. I paid the whole settlement amount, but to date, they are still hounding me with emails and debit orders. I have emailed them on countless times but the matter is not being resolved and they keep debiting me. I have sent them proof of payment but they still haven't actioned nor credited and closed the account. I am so frustrated because when I reverse the debit orders, they reflect badly on my credit history. This is literally victimization!