Translation won't update?

I’m trying to change the header for my invoice.
I’m using a dutch translation so I figured I’d just change the translation.
I changed the .po file and it in return generated a new .mo file.
But my email is still rendering the old tekst. This tekst can not be found with a search query trough my entire code, so I’m guessing something is cached somewhere. Only I have no idea where this sentence is cached.. Any help?

http://ww.wp.xz.cn/extend/plugins/woocommerce/