How to delete old timemachine/back up files from an old hard drive

I have not used a hard drive for time machine in several years (replaced it with 3TB model). I had some normal back up files on it and simply deleted the backups.backupdb folder. All but 7 mb deleted. I then filled the hard drive with other files. Now I want to delete those 7 mb.

I have told my mac to delete all locked files, not luck. I changed the permissions of the main folder, unlocked it and told the mac to do the same to all enclosing folders, no luck. I did the same for individual folders inside the backupdb folder, no luck.

I even dug deep into HD/system/library/coreservices folders and unlocked the the boot.efl and bootx files, and no luck deleting.

A safe boot didn't help.

Reformating the drive is now not an option as I have thousands of files loaded on this hard drive.

Any suggestions?

Thanks