Ok, so I'm selling my PS3 and I've just finished doing a full format ( which took 22 hours) as I read it deletes all data and makes it basically like it's just came out the box. But as all my game data has gone, I'm still signed into the PS3 under my name so I also checked the Playstation network to go online option and my email address was still displayed!? I thought all personal data was deleted? Is there something else I need to do?

use a new user login so that you able to delete the previous one you using...

actually you don't have to waste time formating the system, just delete every contents and delete that account will clear everything away...

Ok that's all sorted, one thing I forgot to do was deactivate the console. Is that possible to do from my ps4?

I'm surprised if you can't do it from your browser anywhere.

Im struggling like crazy finding how to do it from a PC

Delete it

Or email PlayStation support, you can only deactivate once every six months via SONY ENTERTAINMENT NETWORK.
I would of just done a secure erase on the HDD as well.