How to escalate a complaint

I just experienced pretty much the same thing but it was for the S24 promo. I switched my plan 1st with a representative via phone to qualify according to him for the $900 promo. We traded in our devices as well, they had to be for the promo, again according to the rep. I upgraded to a S24 Ultra & the other upgrade was a S24 that I was told would end up being a close to a $10 credit per month since the phone was $799.99 & the promo $900. The extra $100 would be broken into bill credits. The representative reassured me that both phones met the qualifications after changing my grandfathered in plan (I have been a customer since Sprint days 20+ yrs) 

So now I look at my bill & a $600 promo has been applied to both phones & not the $900 as promised. I'm actually being charged now $10 a month for the S24 & instead of under $20 a month for the Ultra, I'm being charged over $30. Even the price of rate plan doesn't match what I was told over the phone that day.

 I call T-mobile & they tell me that the rate plan didn't qualify for the $900 promo so they pick the promo it does qualify for. I said wait a minute this is not right. I was told & reassured one thing while getting something completely different. I took over a page of notes from that call & even when trying to get the agent to try a different promo code that was for $800 that we qualified for according to T-mobiles website & full terms I was told it was phone specific. Though on their website it does not mention this. I took a screenshot of this also. 

Something has to be able to get done about this because these tactics are disgusting & why we lose trust in businesses.