Well, you did something wrong and there were consequences.
Such is life.
I don't know why, but I got my account suspended for 1 month for allegedly voting myself, but I don't remember doing that in the last 1.5 years roughly speaking.
Well - to get a quick dictionary definition of allegedly... "used to convey that something is claimed to be the case or have taken place, although there is no proof."
The only reason I voted for myself from a different account was because someone downvoted like 10 questions in a row, I might be misremembering, but it wasn't to get more reputation points, it was to revert the negative votes I was getting from the same person.
Well that's the very definition of voting fraud.
If someone had 'voted 10 questions in a row' it should have been reverted automatically. If not you should have flagged it for moderator attention. While we can't see who voted for who, the CMs can. That said...
It probably wasn't one vote. Generally there has to be a certain level of obvious fraud, and the moment we're talking about account mergers and suspensions, there's community managers and moderator investigations involved. There's more to the story than "one stray vote years ago".
But after it was found I did that a long time ago, I got suspended and my accounts got merged, I didn't want that, because I wanted to maintain privacy and didn't want people to know that I was the same person for various privacy reasons, so I really think it should have been handled more professionally. They could have disabled my secondary account, because I didn't use it for a very long time, instead of merging it.
Well - that's also a consequence of both your accounts interacting. It might be worth reading and familiarising yourself with how to use alternate accounts ethically on the network
Having an alternate account for privacy or security is fine. You just need to ensure an extremely high level of seperation between them

You broke the rules and honestly, I don't think you've told us the whole story. That said, This should be a learning experience - the moderation team is here to help. If you suspect voting fraud - flag it for attention. If you have an alternate account, NEVER EVER interact with your posts on another account. Don't even interact with the same posts on your accounts. Keep them separate and you should be fine