How to escalate a complaint

Was promised and have in writing via text that if I switched to T Mobile I'd get 2 iPhone 13's on them. Have it on record with 2 different reps that all I'd have to pay is state sales tax which was &135.82 for the full price of the phones. First bill was what I was quoted. 2nd bill was $50 more! Reached out to customer service and was told that the rep gave me an expired promotion but that I was only being charge 50% of the retail price. But I paid 100% in sales tax!!!! Now my husband and I are fighting about this daily as we are living on a fixed income which I made very clear to everyone I spoke to. The stress is nearly unbearable! Now I'm going to have to take my phones back to the store as well as the modem for internet. Get a new bank account number which will cost me but I'll be damned if they steal another dime from me. Find another carrier. This is an absolute nightmare! If anyone is reading this and would like to be a part of a class action respond to this message. I would feel more comfortable dealing with a loan shark than this ridiculous company!!