I do agree with you though, this is not something that should happen, and chipmixer should give clarity faster about your issue, and whether it's a fault on their end, or yours.
I'm taking a guess here, but it's very likely operated by just one person with also other things on his mind. This isn't a traditional business and there is always a risk to ANY centralized entity you send coins to that things can go wrong. I'm confident that ChipMixer will sort it out as usual, but it requires some patience in this case.
This case reminds me of;
https://bitcointalk.org/index.php?topic=5173144.0 where ChipMixer admitted that the error was on their side and as expected the user got his funds.