I had a few hundred dollars (so not a huge debt) written off, without me doing anything. The debt was due to charges (and interest on those charges) applied on a dormant account. The thing is, I didn't know that the charges were accumulating or I would have closed the account. If they had told me, eg, after 6 months or so (seems like a reasonable amount of time to give), I would have paid the $40 or whatever and closed the account. Instead they let the charges accumulate for five years before feeling the need to contact me. So, yeah, I wasn't going to pay that! I was planning on offering to pay whatever the amount would have been after 6 months but then I got a letter stating that they won't pursue the matter. Maybe they realised how ridiculous it was that they didn't contact me sooner.

I wonder did it affect my credit rating, but where I am, credit ratings really aren't all that important compared to the US (and reset over a few years anyway).

Yep, that's a violation of the FDPCA. It was probably more cost effective for them to write it off than to have to deal with you litigating.

Nitpick: It’s the Fair Debt Collection Practices Act, so FDCPA