What you’re saying NameDeck, which is same thing I’m getting at, is that he possibly never had clear title to the domain. He never paid any fees (even though he keeps talking about “payments”). Apparently, he doesn’t have “receipts” (plural) because all that happened was one single transaction where he received control of the domain.
As far as that the domain didn’t exist other than for the one year that he had control of it, that’s conjecture not fact.
Anyway the simple explanation is that the domain belongs to someone else that someone being whoever registered it at some prior date - apparently 2016 - and OP’s “registration” wasn’t a registration of a new domain but rather his picking up what was already registered but not actually expired.
The other explanation is the one offered by OP that there was some vast conspiracy to backdate creation date of the domain and that no one has been paying fees or holding title on the domain since 2016.
Yes, we're on the same page here. I'm not saying the OP has no reason to be pissed off, I know I would be in this scenario but just like you I tend to be looking for the easiest, more logical explanation.
I also take into account the value of the name. If I were to run some elaborate scheme to hack a registry I sure as hell wouldn't target this domain. It's not worth the risk. It might have been the case if I targeted a fair lot of good (not amazing, super premium as that wouldn't go unnoticed) but eventually it would get noticed and I'm sure any registry that would be compromised to this extend would be trending news in no time, especially if it concerns a well established ccTLD like .se.
Op sent me some screenshots from a chat he had with the support. They basically accused him, which usually a support guy won't degrade himself too. I was a pain in the ass this day to their support (same people) and they have been nothing but friendly and accommodating.
I'd love to see a full transcript of that chat to know on what facts their support based their claims so if OP is willing to share them in private I'm willing to review their stance.
Thing is, there's no real solution to this case that OP may find to be satisfactory.
If IIS really was hacked and there's some elaborate scheme going on, suing seems to be the only option. If OP really has the proof he claims he has it's an easy win though and would 100% result in him getting the domain back. Any sane lawyer would take that case. If OP really has the proof he claims he has that is.
If it was registered to him in error while already registered by someone else, sure, the registrar is to blame but he would not have any legal claim to the name, just like xynames stated before.