My phone rebate

Hello, I have been trying for a year, to get mine resolved, I am so upset, I was thinking of just goi g with a whole different company, and I been a long time customer,  im so discussed with this company any more. I have been with you since the note 8 was out. The phone I traded in was the note 9, great phone, I wish I never traded it in , I need to know why have I been told it was recieved and this was in Feb or March of last year, I have tried calling many times, and now I really just want my phone back and I want to leave this company, your always looking for ways to scam the customer and I am not comfortable with you any more . So sick of it during covid it was brought to my attention I was paying 3 yrs for a modem I never had, over charged 3 years only got half back. I really needed that for the phone, thats how I calculated to avoid this phone. It was in mint and it was accepted,  I never got the 400. Credit.

So who do I have to go see to get this resolved? Please let me know. Thank you. 

Patricia [Edited: "Personal Information"]