[Koha] How to clean Koha imported records?

Hello, I am running Koha 3.14. I imported several batches for testing purposes, but I need to delete those records so I go to "Manage staged MARC records" and press on "Clean". When I search the OPAC, I can still see those records as if they were not deleted! I rebuilt zebra as well as restarted the zebra index but still in vain. I need to delete all the previously imported records and start a fresh clean catalogue. Any suggestions would be greatly appreciated. Regards.