Escalation department or top tier customer service management info request, please help!

I’ve ported from T-Mobile to AT&T two days back.
One of the sales executives LIED and gave a false statement to get an extra order in his account. Only based on which I've ordered an Iphone11 with a trade in over the same call. Now due to that, AT&T is asking me to pay 75$/month more than my budget, though the sales rep in the call assured that I can switch to a 30$/month plan without affecting my billing credits.
Being just a STUDENT, no service associate is neither understanding the issue that as a student I cannot afford 75$ month or even 50$/month for a mobile bill. I'm managing both my education and bill with my part time jobs, which by itself is really difficult. I really feel bad and frustrated with the repeated calls and hoping someone would understand my situation and help through the issue. My maximum budget for a mobile is about 30$/month, I would really be grateful, if this issue can be solved, please