Hello. Gave up after reading the thread, but gladly this has been resolved.
The Bitmixer support team sent me a mail which is "Sorry again for the issue, all admins were on vacations. I've transferred 30 + 5 btc as a compensation. Thank you.".
They gave me a happy new year present

Thank you.

Surely.

Address : 18hs5EFFkShXAkz89xJspYWmWP6emjdHf5
Message :
This is my address.
https://bitcointalk.org/index.php?action=profile;u=708542
Signature :
H6ps2isLveeYTe6Fipw5U7T3rwOXbiyrdGVuobzvE7qWdG0U0QH2/ySBdLMZEaVTrRN2ULvZgWHjt7uqYPwbx7U=


Address : 12anNurKoyqUUbovPi5KVWFprrRtdybf3w
Message :
This is my address.
https://bitcointalk.org/index.php?action=profile;u=708542
Signature :
H6J7leiPzrwTokue28HbNmsqckEPH0V5ewLPUkpGlWGbehP9OD9RM+zpqkUo4cu0nvU5AiuyEJmMk+1VAeDBVIE=


Address : 1qvAJb8i4AhdAuA3Ui2NhdtAxKEhrVCUW
Message :
This is my address.
https://bitcointalk.org/index.php?action=profile;u=708542
Signature :
HzbmILcmH6Yc7tH58wmbgH/Zt2Dsq2/RCpEtLc1R/2l7HLcbaAEaO+rlKGXWLxrR22oER8jwLnDY1z3Aoje0z2E=


Address : 1G6JGHWgsDuF2yUSaReTr2gVKXcaqiK93t
Message :
This is my address.
https://bitcointalk.org/index.php?action=profile;u=708542
Signature :
H2cTvOXhdVcnbnjAqS0Jgo2mgNXGi5V0YAJYM4sa5tXXVhDto2Y0mZHNjcnYiQ3Di0BJhSjvbQryqul oVC3vUFw=

this is accident transaction id
https://blockchain.info/tx/edaa17afa27845bb26fb08bd9147080bc8440e3439d43ac2e29ebef61ea65025

And I send email it was my mistake and I will send 0.123 BTC more with one of source Address,  I send 0.123 BTC after send email

https://blockchain.info/tx/f355a301bacc4791d9fb0387476fadf25b2987a3219df594e28008a7e4eb4f5b

this is full of email.

#1
I miss send to my bitcoin to 1BitmixerEiyyp3eTLaCpgBbhYERs48qza
How i can back my coin?

------------------
Submitted from: https://bitmixer.io/contacts.html

#2 - i sent this email before send 0.123 BTC.
I will proof my address with send tip to 0.123 with one of source address ( 18hs5EFFkShXAkz89xJspYWmWP6emjdHf5 )
and give me my coin back to one of my source address thx.

#3
Hello,

Sadly there is nothing that we can do.

Best,

Josh

#4
that is your tip address but why nothing you can do?

#5
Hello,

All funds sent to this address are considered donations.

Best,

Josh

#6
Wow.. I was user of bitmixer.io but i just mistake send that because that address in letter of guarantee.

whatever donator told that is mistake and please return that coin but you don't want to return the coin right?

I will donate 30 percent please return 70percent.

#7
Hello,

I am sorry you sent to the wrong address, but their is nothing I can do.

Best,

Josh

#8
Ok i will share this support to bitcointalk and reddit.

#9
Hello,

Okay, I am sorry I can not help any further.

Best,

Josh

https://blockchain.info/tx/edaa17afa27845bb26fb08bd9147080bc8440e3439d43ac2e29ebef61ea65025

this is transaction ID.

I already proved my bitcoin address via email

but they told me "Sadly there is nothing that we can do."

Yesterday, Bitmixer.io sent me a message that signed with Bitcoin address and I mistakenly sent 30 BTC to that address. It turns out they are using that address for receiving donations, so I immediately contacted the Bitmixer.io team with solid proof asking for refund.
But they are keep saying "Sadly there is nothing that we can do." and "All funds sent to this address are considered donations.”

I replied "It was absolutely not a donation. But that was my mistake, I will donate 30% of mistakenly sent BTC so can I get the rest of them back", but they replied "I am sorry you sent to the wrong address, but there is nothing I can do.”

This is absolute nonsense and pathetic. Even though this is happened because of my mistake, it seems they care more about their earnings (whether it is legit or not) than the customers. If you are thinking of using Bitmixer.io with large amount of Bitcoin, please aware that there is a possibility of scam.