UNWANTED SPAM CALLS AND MESSAGES - HOW DO I BLOCK THEM FOR GOOD!!!

Been getting numerous voice mails from 805 637 7243. This is the so-called number to call to check voice mails for T-Mobile? I usually dial my cell phone number for voice mail access. I blocked this number as well as 305-707-0225 where the voice mails appear to originate from. The blocks are NOT working!! I'm getting calls, with no ring, and just noticing the voice mails. How can I stop getting any calls/messages and annoyances from these spammers???