Upgrade costs more than a new phone?

I currently have the Z flip 3 and wanted to upgrade to he flip 5, Tmobile had a promotion available for Magenta Max (which is the plan that I have). This promotion was allowing me to upgrade my phone, I called the representative and she said that for that offer to work I would have to pay off my current device which had 2 payments left, so I payed the amount, and she said to call tomorrow and that I should be able to upgrade. I called today and the representative told me that I still had an installment due before I'm able to upgrade my device, mind you I had already received an email and pdf stating that my device was payed off, I asked for the amount and the total would only be justified if it was for my watch. I've had issues with them before, the representative that helped me purchasing my phone said that the watch device would be free of charge if I enrolled in their Magenta Max plan and got a line for it, I did just that and noticed that they had been charging me for the device monthly, I just payed for it because of the benefits the representative told me, where included in my plan which also allowed me to upgrade my phone. Coming to today, the representative told me that would have to pay the extra installment which does not make sense AND change my plan for me to be able to upgrade, which leaves me thinking why was I even paying for the previous plan, I asked if then I could change my line to something less expensive as now all purpose of the plan was gone and he just told me I could only get the newer plan which increases the price by $30. I had seen the essential plan online so his answer left much to wish for. Has anyone else had similar issues? And if so how did you resolve it?