Existing organization getting updated instead a new organization
This appears to be a bug and you should report it in GitLab.

Steps to replicate.

Set up Contribution page using 'on behalf of'

Submit the form a first time, create your 'on behalf of' Org

Submit the form a second time for New Org, using new name/email.

Outcome the original Org now has the new email but the old name. Both contributions are on their record.

Testing was done via http://dmaster.demo.civicrm.org/civicrm/contribute/transact?reset=1&amp;id=4 (which will soon disappear)

Update - There is now a patch submitted and an issue filed in GitLab - https://lab.civicrm.org/dev/core/issues/26