Lied to about promotion

In April of 2024, my oldest daughter and I went in to our local T-Mobile store to get her a new phone for her birthday. We talked about the promotions they had and we were trading in her like new old iPhone in for a new one. They didn't have the one she wanted at the store so they suggested we call customer service. We spent almost TWO HOURS on the phone ordering her new iPhone. We double and triple checked about the promo and that her phone credit would go towards her new phone payments and what those payments would be. Instead, we get a credit on our actual bill instead of towards the phone payments. I called to get it straighted out. They say they are fixing it but it doesn't get fixed. I called back. I was then told that there was no promo and the way the phone was traded in, the only way a credit could be given is an account credit. After about three weeks of back and forth,  I am told that it will actually be done and the credit will be applied correctly. Nope... they put the money towards my other daughters phone, as if she made a lump sum payment, and we are still paying full price every month for the other phone. I am just, completely DONE!