Did your instance of Electron Cash start up on the right block chain? Follow this guide to be sure (as of this post the BCC block height is 478609 vs 478918 for BTC):

https://www.reddit.com/r/btc/comments/6qyn18/electroncash_notice_how_to_select_bitcoincash/

Ok, I followed the advice and got it done.

First off follow the advice about electron cash.  There are too many red flags and if you have a large amount of Bitcoin that you cannot stand to lose do steps to protect yourself.

Install electron cash on a computer that doesn't have your Bitcoin wallet or any information about your Bitcoin. Use a virtual machine if you can.

When you get to the option to select new wallet etc. Select you have a existing seed or master seed. This is your list of twelve words that you got when you did a backup of your Mycelium wallet

Type the words in with spaces. Example "one two three four five six seven eight nine ten eleven twelve"

You'll notice that the next box in the lower rightbcorner is greyed out

Click the Options box. Put a check in the BIP138 box

Now the next box is available. Click next and when the wallet connects to the Bitcoin cash server you will see your Bitcoin cash balance.

I strongly suggest you transfer the Bitcoin cash out to an exchange that supports Bitcoin cash transfers.

Delete the electron cash wallet after you transfer the Bitcoin cash out and if your really paranoid reformat the computer.  If you used a virtual machine then no worries

EMPTY the Mycelium Wallet back to the exchange Coinbase etc or to another Bitcoin Wallet

Now do what you'd like with the Bitcoin cash. It's free money