Selena Gomez -- I'm Blocking Justin Bieber From My Life

Selena Gomez spent the last day blocking her phone numbers and other communication devices so Justin Bieber cannot contact her ... TMZ has learned.

Sources familiar with the situation tell TMZ ... Selena wants no contact with Justin, so whatever they tried hashing out during their sit-down last Sunday didn't work. She has blocked her phone (which includes texting). For some reason, she's still following Justin on Twitter, but we're told she's blocked him on all forms of contact.

And ... we've learned ... the breakup absolutely, positively involved another woman -- though our sources didn't know which one. There's been speculation that it's a Victoria's Secret model. We don't know for sure if it's her, but we know it involves another woman.