reception issues iphone 13

Having serious reception issues downtown Sacramento California zip 95814.

called T-mobile and first they asked me to reset network setting on my phone. that didn’t do anything to improve.

next, they said i needed to upgrade the sim card to enable 5G. i did and still the same issue. calls are erratic and disconnect easily, as well as messages.

there is no WIFI inside the building that I work in, so i cannot use any app either (like facebook, apple music, etc.).

any help?

gracias