Bug / data protection issue new customer

Recently installed a clean version of 3.0.2.0 using original sql database (previously using older version of opencart - 2.1.01?).

Then tried to upload the backup I took before upgrading - said it failed 500 error

According to opencart's admin interface all my previous customer, product and settings data were gone forever.

Manually re-set everything up except customers (settings, added products, etc), everything looked to be working perfectly :-)

Then I decided to do a test purchase and registered myself as a new customer. All good until it asked me if I wanted to ship to the address in my address book and showed me the name and address of one of my original customers

Tried again using an incognito browser window (hoping that something locally was going wrong - clutching at straws!) and registered another new test customer - same thing again, address book had full name and address of a different one of my original customers

Massive data protection breach if I let the "new" site go live.

Wanted to report the bug and also ask where to go in and manually delete this old ghost data?

Thanks

UPDATE

Managed to log onto sql database and have a poke around in there. Looks like the clean installation of 3.0.2.0 deleted all data prior to the installation date except:-
Customer address details from 2015 (original install date) to date - linked to customer number so had simply appended to the newly created customer details when OC re-used the customer numbers.
Paypal transaction details - 2 separate files

Have manually deleted all old data I could find and seems to have fixed the issue.