Caller At 559-790-5674 Refuses To Stop Contacting me!

It has been almost a year... & the unknown caller/stalker at (559-790-5674) who goes by the name "Tristan" refuse to stop contacting me!  - I assigned that number to be blocked & noted I was getting text messages and voicemails again... the phone company said it is because the caller is not sending the messages from a phone but from an APP....