A problem I had on my Mac using rbenv was that when I first set it up, it loaded a bunch of ruby executables in /usr/local/bin - these executables loaded the system ruby, rather than the current version.
If you run
which bundle
And it shows /usr/local/bin/bundle you may have this issue.
Search through /usr/local/bin and delete any files that start with #!/user/bin ruby
Then run
rbenv rehash