The short answer
Combine carrier filtering, phone settings, careful reporting, and stronger account habits; no single setting stops every unwanted contact.
Step by step
Enable the carrier's current spam-call protection and the phone's unknown-caller or spam-filtering features.
Block and report repeated senders through the calling or messaging app instead of replying.
Do not follow unexpected links, provide account codes, or call a number supplied in a suspicious message.
Register eligible numbers with the national do-not-call service, while recognizing that criminals may ignore it.
For messages claiming to be from a carrier, bank, or agency, open the official app or type the known website yourself.
Before you finish
Keep screenshots, receipts, chat transcripts, confirmation numbers, and the first bill after a change. Carrier terms and account eligibility can change, so verify the final price and conditions directly before submitting an order.