Advanced Tier 2 support required

I had a trade in approved for $830 in February for my IPhone 15 pro with IPhone 17 pro that O bought in January this year. In March, your team credited 330$ saying that you are eligible for this trade -in amount and will have to pay for rest of the monthly payments.

i am under unlimited line contract since last 3 years and when approached for trade in on January said you are eligible with unlimited line too and deactivated unlimited line as I already have two unlimited lines. Now in July they say that we cannot apply promotion as you do not have unlimited premium line. I am at a loss of 500 dollars as my 15 IPhone pro has been a new one I purchased from Xfinity and I would not trade in if it going as low as 330$. Please help as I am frustrated with your customer support. Please refer to my case history from January, February and March this year.