Bad horrible poor service

I have received the worst service from Rentoza. I subscribed for a 6months subscription and paid the buyout price after the 6 months. Now I have been requesting them to remove ownership software on the phone with no success. It’s been a whole month of back and forth and it seems like no one knows what to do. To say I am frustrated is actually an understatement. Why can’t this software be removed from the phone once the certificate of ownership is issued. I will never ever use Rentoza. At the moment I am being ignored I am sending emails and WhatsApp but no one is addressing my concerns