If your email template looks something like the one below, something is wrong.
Try temporarily disabling your chrome extensions. To do this type "chrome://extensions/" in your chrome address bar. Refresh your spreadsheet and restart Wizy Doc and Mail Merge add-on.
If this works, detect which chrome extension is causing the trouble and put it in the bin.
Your Wizy Doc and Mail Merge template page should look like the one below, with a drop down Available Tags menu