how to stop spam calls from 805 637 7243

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???

Have you tried long pressing the number on the dialer and there should be an option for block/ report spam.

The caller can still leave a voicemail though.

That is literally the T-Mobile voicemail number. I have no idea why it was implemented this way, but it's telling you that there is an unheard vm in your box. Maybe a call you rejected or a blocked number? You can't block it because it's the voicemail service. 

This T-Mobile support page shows that it is the T-Mobile voicemail system