Excel Services and Office Web Apps

Be aware that if you would like to use Excel Services for rendering your Excel files instead of using Office Web Apps, you would have to suppress the WOPI Binding that is responsible for viewing of Excel files. This is done through PowerShell in the SharePoint farm, it’s not a WAC setting.

New-SPWOPISuppressionSetting -extension XLSX -Action View

This command will suppress the WOPI Binding for the extension XLSX (Excel files) and for the WOPI ActionView.

It not necessary to iisreset on the SharePoint farm or even the Wopi farm or anything else.

But if you want to check if your files are rendered using WAC or Excel Calc you can take a look to the url showed.

If its viewed using Office Web Apps the URL will look something like this:
https://server/_layouts/15/WopiFrame.aspx/sourcedoc=/Documents/excel.xlsx
but if Excel Calc is rendering the document it should look like the following:
https://server/_layouts/15/xlviewer.aspx?id=/Documents/excel.xlsx

You can also check the WOPI suppression settings using the command Get-SPWOPISuppressionSetting

Finally, If you need to revert your changes, use the command Remove-SPWopiSupressionSetting

Update 2016/05/24: Additionally if any of this works, try to use the commando Remove-SPWopibinding -application “excel” this will remove all the Excel binding in the Wopi farm

Hope it helps!