Since this question seems to be gaining traction again.
I’m really sorry, but it sounds like you may have been the victim of a phishing attack (link from Slack, Reddit, Forum, Google Ad, etc.), malware, remote-access hack (e.g. via Teamviewer), or something similar. I cannot easily tell you how this could have happened without exactly knowing what you do.
MyEtherWallet.com is a client-side wallet, which means you hold your keys. If someone gets your private information (private key, keystore file, mnemonic, passwords), they have complete access to your funds. There is no stopping transactions, canceling transactions, or resetting passwords on the blockchain. Once a transaction is on the blockchain, it's final.
This is why you must be diligent about the safety and security of your private key. Just like you wouldn't enter your credit card information into a random site or click a random link in your email, you shouldn't enter your private key into a random site or click a random link in your DM.
There are people who follow, track, and attempt to shut down the people behind these sites. We at MyEtherWallet do what we can to warn others, take down the site, and notify exchanges of confirmed addresses and information.
Document & Collect Information
Look through your history for any URLs that look like MyEtherWallet.com (or any other crypto-related site) but are actually a very similar URL (e.g. myetherwallet[.]su or myetherwallet[.]com[.]co).
Document your Ethereum address, transaction hashes, and malicious website or malware or wahtever it was.
Document how you got to this link. Was it on a forum? Posted to reddit? In a Slack DM?
Screenshots, if available, are good of the message sent and the malicious website. Screenshots of your address or transaction should always be accompanied by text / links to them on etherscan.io. No one wants to hand-type an address from a screenshot..
If the website is related to MyEtherWallet, we want to know so we can add to our documentation and records. You can email us at support[at]myetherwallet.com
Move your Funds ASAP
Protect Yourself Moving Forward
Get the Malicous Website Taken Down
Again, I'm really sorry.