Don't you find weird that this address has already been used 6 times since October? I don't think you can be "100% sure" that this wasn't a mistake on your end.
I think its actually quite convenient. If I was chipmixer and I was going to selectively scam people, this is exactly what I would do so people like you would say that. It's all about creating a scenario in which it looks "unrealistic" to get away with it.
From what I've seen, it's much more likely you just somehow used the wrong website. There are several phishing sites out there.
I had like 12, 13 sessions in a row for close to 2 hours just fine right before this issue. the ONLY way would've been for me to mistype the domain and for me to not realize it, even though I make a conscious effort to look at the URL every single time.
Making a small typo once every few hours doesn't sound too far fetched
