I recently picked up a second-hame copy of a pokemon game from a well known game store franchise. I made this purchase using my loyalty card for the store. When I got home, I reset the cartridge so I could start my own playthrough (pokemon games only have one save slot, so it's necessary to remove the old save before restarting). I did briefly check the save file to see if there were any interesting pokemon, but ended up just resetting because everything was pretty standard (apart from the surfeit of pidgeys).

A few days later, I got a call from the store telling me there was an issue with the sale, and that there was someone who wanted to talk to me. I said okay, and the sales associate handed the phone over to a kid (primary school aged). Turned out it was his game, and he was pretty upset (he'd sold it, but regretted it, as far as I could work out).

Now, I'd lost a couple of pokemon games when I was young, and it was pretty upsetting, so I felt for the kid. We talked for a few minutes and I agreed to give him the game back in exchange for what the store had originally given him (quite a lot less than what I had paid the store), but apologised and told him that I'd already written over the save file so it was only the game he'd be getting back. He said he understood, and I asked him to pass me to his Mum, and I cleared both the exchange and the fact that the cartridge would be blank when it was returned with her. We arranged to meet at the store a few days later.

The hand over went fine, the kid seemed really happy to have his game back and started a new game while still in the store. The Mum thanked me, gave me the money, they left, and I didn't think any more of it beyond trying to track down another copy (it's a slightly older game).

A few days later I started getting calls from the kids Dad, yelling at me and accusing me of 'stealing' his son's pokemon, that some of the pokemon on the cart had been rare/hard to get and they'd had to go to certain places for the events to get them and that had cost money, etc. I talked for him just long enough to ascertain how he'd gotten my number (apparently the store clerk gave it to them after my call with the boy and his Mum, which I did not agree to and in fact arranged the store as the meeting place to avoid giving them my personal data) and then told him I had legally purchased the game and had done nothing wrong.

He continued to call incessantly (43 calls in three days) and sent multiple texts. I did not answer or reply. Eventually, I sent him a text telling him to cease contacting me and that any further contact would be considered harassment, and blocked his number. I did not delete his texts or the calls in my call log and am in the process of backing up my voice mail messages.

On Friday I got a letter by registered mail saying I owe >$2400 for destruction of property by the end of January and that failure to pay would result in further legal action. It included a list of expenses for the costs involved in getting some of the event pokemon (gas to stores, time, etc) but also the cost of their holiday to Japan where they apparently got one of the pokemon. There were no event pokemon on the cart when I got it. The letter was on official looking letterhead from a law firm. Googling the law firm showed they were legit.

I called the firm to find out what was going on, and they said they didn't have a lawyer by the name on the letter working there. They asked me if I could bring the letter in to them and provide any information I had about the guy and that they would like me to provide a statement.

I don't know what to do at this point. I want to help the firm, but I don't feel like it's a good idea to hand over the proof that he did this and I'm not sure if I'm allowed to give them his phone number etc. They're lawyers but not my lawyers, so they're looking out for themselves first, and while I completely understand that, I don't want to get screwed in the middle. Do I give it to them? Do I give them a certified copy instead? Is there any reason I shouldn't give it to them?

I also don't know what to do about this guy if he's willing to go to these lengths, or what to do about the store giving out my personal contact details without permission.