selenium clear() command doesn't clear the element

I don't know the exact reason for your element keeping its value, but you can try an alternative text clearance by sending 'Ctrl+A+Delete' key combination using sendKeys method of the element's object:

emailAddress.sendKeys(Keys.chord(Keys.CONTROL,"a", Keys.DELETE));

It's possible that the fields you're trying to fill has autocomplete attribute set to on. [Reference]

If clear() works when the line executes then it's safe to say that this is not a webdriver specific issue.

It would help if you can show the html snippet of the page section you're working on.

Possible areas of debugging:

forcefully remove autocomplete attribute on page load using java script executor

turn off autocomplete setting on the driver level. I believe the solution would vary depending on the driver being used.

Good luck!

PS: Those Thread.sleep(s) are not advisable.

I had a similar issue with a text field that used an auto-complete plugin. I had to explicitly clear the attribute value as well as do a SendKeys. I created an extension method to encapsulate the behaviour, hopefully the snippet below will help:

public static void SendKeysAutocomplete(this IWebElement element, string fieldValue)
{
   element.SendKeys(fieldValue);
   element.SetAttribute("value", fieldValue);
}

public static void SetAttribute(this IWebElement element, string attributeName, string attributeValue)
{
   var driver = WebDriverHelper.GetDriverFromScenarioContext();

   var executor = (IJavaScriptExecutor)driver;
   executor.ExecuteScript("arguments[0].setAttribute(arguments[1], arguments[2]);", element, attributeName, attributeValue);
}