Why did Tmobile start charging me the 3rd line and the customer service can't solve my problem?

I’ve been on the Magenta Max plan since Oct/2021. I got the promotion, pay 2 lines, and got the 3rd line free.
From Oct/2021 until Aug/2022, everything was right, but someone from T-Mobile did something wrong with my account,  and since September 2022 I have been charged the 3rd line, every time that I contacted customer service I have the promise that the next bill cycle I will have my problem fixed it, but we are now in 2023, and I still have the same issue. The last time, the assistant said that I was removed from the promotion getting as free my 3rd line, but he didn't know how to explain how I cancel the 3rd line if I still have three lines since I joined T-Mobile ( the same numbers) . The assistant said that they need open a " ticket"  for another team to investigate the issue, but according to her, she can't provide the ticket number to me ( T-mobile can check all my case reading the customer service chat). I just want my 3rd line free, the reason for me to switch  from Verizon to T-Mobile and the refund for the last 5 months that I have been paying for the 3rd line, wasting my time to explain all my case, customer service just giving me promise but never real solution. 
Who or Where I should contact to have someone fix the problem in my account anf have my 3rd line free as was in my original agreement? 
i'm very disappointed with T-Mobile, i'm not asking nothing more that was promissed to me, I feel disrespected and deceived; every time I waste my time explaining everything that happened, I received apologies and promises that my problem will be solved in the next billing, and every month I have the disappointed that the problem persists.