RCS cannot fix their APP

Good day, i sent an email to *** in June 2021 to get assistance with my APP. I explained that i changed a phone and dont have access to my previous device and therefore i cannot unlink the device. Today i get a call from a lady to ask me that IT said she must ask me if i tried to unlink the device from the APP. On the initial email i even attached screen shots of the error i get when i try to unlink the devices on the APP, now i fail to understand where the problem is. Are you failing to fix your APP and assist users? from June i have not had any response and i keep sending emails but nothing. Your IT is so *********** as ive been sitting with an APP which i cannot use and you guys are also unable to assist. What should we do if you cannot assist with your own APP?