Overcharging. not getting what I promised during adding a line

Hola,
Awful experience with T-Mobile.
Back in November, I added a line with iPhone 15 pro max that time the tmobile chat representative gave me a breakdown that my bill would be $175 including four lines and total 4 phone payment. But in December my bill came out much higher than 175$. In February  2 of  my phone paid off and march 3rd phone was paid of but my bill instead of decrease it keep increasing. It's been 7 month i talk to serval times and show the tmobile chat they didn't listen and billing extra. I filed a complaint but no response from them. I followed up multiple but no feedback.