Is Data on phones partitioned?

[AC Question]

I'm upgrading my phone, and since my old Samsung android phone still works fine, it's a shame to just bin it. But given I'm not very tech-savvy and always worried about computers, data, and theft, I want to make sure that this phone is scrubbed of any personal contacts, photos and texts that I've made and received. So are there any tech-savvy friends out there can help?

Basically, I've hard reset, then filled up the internal memory with old music and a handful of old generic photos (or filled as much as I can) to essentially scrub it, then hard reset again. Will this have overwritten aforementioned personal contacts, messages and suchlike, or is data partitioned?

I'm happy to pass this phone onto a second-hand shop or whatever and get maybe a few pennies for it (I could really do with a bit of spare cash right now tbh), but given data theft issues, I want to be careful.

Any advice would be appreciated.

 

[Rukbat]

Reflash the ROM (it's so easy with Samsung phones, it's boring - see [Samsung] How to flash Stock ROM via ODIN) and it's almost impossible to recover any data from it. (Suggestion if your wallet can afford it - donate it to a shelter for battered women [with the charger, of course].)